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Introduce the for_each_set_nbits macro

PATCH RESEND In review Syed Nayyar Waris 3 participants 6 messages Apr 2, 2021 – Apr 8, 2021

Subsystems (5)

v4 of 12 In review Latest is v12 →

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#0 lore raw

v4 cover Introduce the for_each_set_nbits macro

Hello Bartosz,

Since this patchset primarily affects GPIO drivers, would you like to pick it up through your GPIO tree?

This patchset introduces a new generic version of for_each_set_nbits. The previous version of for_each_set_clump8 used a fixed size 8-bit clump, but the new generic version can work with clump of any size but less than or equal to BITS_PER_LONG. The patchset utilizes the new macro in several GPIO drivers.

The earlier 8-bit for_each_set_clump8 facilitated a
for-loop syntax that iterates over a memory region entire groups of set bits at a time.

For example, suppose you would like to iterate over a 32-bit integer 8 bits at a time, skipping over 8-bit groups with no set bit, where XXXXXXXX represents the current 8-bit group:

    Example:        10111110 00000000 11111111 00110011
    First loop:     10111110 00000000 11111111 XXXXXXXX
    Second loop:    10111110 00000000 XXXXXXXX 00110011
    Third loop:     XXXXXXXX 00000000 11111111 00110011

Each iteration of the loop returns the next 8-bit group that has at least one set bit.

But with the new for_each_set_nbits the clump size can be different from 8 bits. Moreover, the clump can be split at word boundary in situations where word size is not multiple of clump size. Following are examples showing the working of new macro for clump sizes of 24 bits and 6 bits.

Example 1:
clump size: 24 bits, Number of clumps (or ports): 10
bitmap stores the bit information from where successive clumps are retrieved.

     /* bitmap memory region */
        0x00aa0000ff000000;  /* Most significant bits */
        0xaaaaaa0000ff0000;
        0x000000aa000000aa;
        0xbbbbabcdeffedcba;  /* Least significant bits */

Different iterations of for_each_set_nbits:-
'offset' is the bit position and 'clump' is the 24 bit clump from the above bitmap.

Iteration first:        offset: 0 clump: 0xfedcba
Iteration second:       offset: 24 clump: 0xabcdef
Iteration third:        offset: 48 clump: 0xaabbbb
Iteration fourth:       offset: 96 clump: 0xaa
Iteration fifth:        offset: 144 clump: 0xff
Iteration sixth:        offset: 168 clump: 0xaaaaaa
Iteration seventh:      offset: 216 clump: 0xff

Loop breaks because in the end the remaining bits (0x00aa) size was less than clump size of 24 bits.

In above example it can be seen that in iteration third, the 24 bit clump that was retrieved was split between bitmap[0] and bitmap[1]. This example also shows that 24 bit zeroes if present in between, were skipped (preserving the previous for_each_set_macro8 behaviour).

Example 2:
clump size = 6 bits, Number of clumps (or ports) = 3.

     /* bitmap memory region */
        0x00aa0000ff000000;  /* Most significant bits */
        0xaaaaaa0000ff0000;
        0x0f00000000000000;
        0x0000000000000ac0;  /* Least significant bits */

Different iterations of for_each_set_nbits:
'offset' is the bit position and 'clump' is the 6 bit clump from the above bitmap.
Iteration first: offset: 6 clump: 0x2b
Loop breaks because 6 * 3 = 18 bits traversed in bitmap. Here 6 * 3 is clump size * no. of clumps.

Changes in v4:
- [Patch 3/3]: Remove extra line and add few comments.
- [Patch 3/3]: Use single lock (and unlock) call instead of two lock (and two unlock) calls.
- [Patch 3/3]: Use bitmap_from_arr32() where applicalble.
- [Patch 3/3]: Remove unnecessary 'const'.

Changes in v3:
- [Patch 1/3]: Rename for_each_set_clump to for_each_set_nbits.
- [Patch 1/3]: Shift function definitions outside 'ifdef CONFIG_DEBUG_FS' macro guard to resolve build (linking) error in xilinx Patch[3/3].
- [Patch 2/3]: Rename for_each_set_clump to for_each_set_nbits.

Changes in v2:
- [Patch 1/3]: Shift the macros and related functions to gpiolib inside gpio/. Reduce the visibilty of 'for_each_set_clump' to gpio.
- [Patch 1/3]: Remove __builtin_unreachable and simply use return statement.
- Remove tests from lib/test_bitmap.c as 'for_each_set_clump' is now localised inside gpio/ only.

Syed Nayyar Waris (3):
gpiolib: Introduce the for_each_set_nbits macro
gpio: thunderx: Utilize for_each_set_nbits macro
gpio: xilinx: Utilize generic bitmap_get_value and _set_value

 drivers/gpio/gpio-thunderx.c | 13 ++++--
 drivers/gpio/gpio-xilinx.c   | 52 ++++++++++-----------
 drivers/gpio/gpiolib.c       | 90 ++++++++++++++++++++++++++++++++++++
 drivers/gpio/gpiolib.h       | 28 +++++++++++
 4 files changed, 152 insertions(+), 31 deletions(-)

base-commit: e1b7033ecdac56c1cc4dff72d67cac25d449efc6

Signature · 1 line
2.29.0
#1 lore raw

PATCH RESEND v4 1/3 gpiolib: Introduce the for_each_set_nbits macro

This macro iterates for each group of bits (clump) with set bits, within a bitmap memory region. For each iteration, "start" is set to the bit offset of the found clump, while the respective clump value is stored to the location pointed by "clump". Additionally, the bitmap_get_value() and bitmap_set_value() functions are introduced to respectively get and set a value of n-bits in a bitmap memory region. The n-bits can have any size from 1 to BITS_PER_LONG. size less than 1 or more than BITS_PER_LONG causes undefined behaviour. Moreover, during setting value of n-bit in bitmap, if a situation arise that the width of next n-bit is exceeding the word boundary, then it will divide itself such that some portion of it is stored in that word, while the remaining portion is stored in the next higher word. Similar situation occurs while retrieving the value from bitmap.

Cc Linus Walleij <[email protected]>
Cc Bartosz Gołaszewski <[email protected]>
Cc Arnd Bergmann <[email protected]>
Cc Andy Shevchenko <[email protected]>
---
 drivers/gpio/gpiolib.c | 90 ++++++++++++++++++++++++++++++++++++++++++
 drivers/gpio/gpiolib.h | 28 +++++++++++++
 2 files changed, 118 insertions(+)
drivers/gpio/gpiolib.c +90 -0
index 1427c1be749b..5576d1465c81 100644
@@ -150,6 +150,96 @@ struct gpio_desc *gpiochip_get_desc(struct gpio_chip *gc,
 }
 EXPORT_SYMBOL_GPL(gpiochip_get_desc);
 
+/**
+ * bitmap_get_value - get a value of n-bits from the memory region
+ * @map: address to the bitmap memory region
+ * @start: bit offset of the n-bit value
+ * @nbits: size of value in bits (must be between 1 and BITS_PER_LONG inclusive).
+ *
+ * Returns value of nbits located at the @start bit offset within the @map
+ * memory region.
+ */
+unsigned long bitmap_get_value(const unsigned long *map,
+				unsigned long start,
+				unsigned long nbits)
+{
+	const size_t index = BIT_WORD(start);
+	const unsigned long offset = start % BITS_PER_LONG;
+	const unsigned long ceiling = round_up(start + 1, BITS_PER_LONG);
+	const unsigned long space = ceiling - start;
+	unsigned long value_low, value_high;
+
+	if (space >= nbits)
+		return (map[index] >> offset) & GENMASK(nbits - 1, 0);
+	else {
+		value_low = map[index] & BITMAP_FIRST_WORD_MASK(start);
+		value_high = map[index + 1] & BITMAP_LAST_WORD_MASK(start + nbits);
+		return (value_low >> offset) | (value_high << space);
+	}
+}
+EXPORT_SYMBOL_GPL(bitmap_get_value);
+
+/**
+ * bitmap_set_value - set value within a memory region
+ * @map: address to the bitmap memory region
+ * @nbits: size of map in bits
+ * @value: value of clump
+ * @value_width: size of value in bits (must be between 1 and BITS_PER_LONG inclusive)
+ * @start: bit offset of the value
+ */
+void bitmap_set_value(unsigned long *map, unsigned long nbits,
+			unsigned long value, unsigned long value_width,
+			unsigned long start)
+{
+	const unsigned long index = BIT_WORD(start);
+	const unsigned long length = BIT_WORD(nbits);
+	const unsigned long offset = start % BITS_PER_LONG;
+	const unsigned long ceiling = round_up(start + 1, BITS_PER_LONG);
+	const unsigned long space = ceiling - start;
+
+	value &= GENMASK(value_width - 1, 0);
+
+	if (space >= value_width) {
+		map[index] &= ~(GENMASK(value_width - 1, 0) << offset);
+		map[index] |= value << offset;
+	} else {
+		map[index + 0] &= ~BITMAP_FIRST_WORD_MASK(start);
+		map[index + 0] |= value << offset;
+
+		if (index + 1 >= length)
+			return;
+
+		map[index + 1] &= ~BITMAP_LAST_WORD_MASK(start + value_width);
+		map[index + 1] |= value >> space;
+	}
+}
+EXPORT_SYMBOL_GPL(bitmap_set_value);
+
+/**
+ * find_next_clump - find next clump with set bits in a memory region
+ * @clump: location to store copy of found clump
+ * @addr: address to base the search on
+ * @size: bitmap size in number of bits
+ * @offset: bit offset at which to start searching
+ * @clump_size: clump size in bits
+ *
+ * Returns the bit offset for the next set clump; the found clump value is
+ * copied to the location pointed by @clump. If no bits are set, returns @size.
+ */
+unsigned long find_next_clump(unsigned long *clump, const unsigned long *addr,
+				unsigned long size, unsigned long offset,
+				unsigned long clump_size)
+{
+	offset = find_next_bit(addr, size, offset);
+	if (offset == size)
+		return size;
+
+	offset = rounddown(offset, clump_size);
+	*clump = bitmap_get_value(addr, offset, clump_size);
+	return offset;
+}
+EXPORT_SYMBOL_GPL(find_next_clump);
+
 /**
  * desc_to_gpio - convert a GPIO descriptor to the integer namespace
  * @desc: GPIO descriptor
drivers/gpio/gpiolib.h +28 -0
index 30bc3f80f83e..af79784dfce3 100644
@@ -141,6 +141,34 @@ int gpio_set_debounce_timeout(struct gpio_desc *desc, unsigned int debounce);
 int gpiod_hog(struct gpio_desc *desc, const char *name,
 		unsigned long lflags, enum gpiod_flags dflags);
 
+unsigned long bitmap_get_value(const unsigned long *map,
+				unsigned long start,
+				unsigned long nbits);
+
+void bitmap_set_value(unsigned long *map, unsigned long nbits,
+			unsigned long value, unsigned long value_width,
+			unsigned long start);
+
+unsigned long find_next_clump(unsigned long *clump, const unsigned long *addr,
+				unsigned long size, unsigned long offset,
+				unsigned long clump_size);
+
+#define find_first_clump(clump, bits, size, clump_size) \
+	find_next_clump((clump), (bits), (size), 0, (clump_size))
+
+/**
+ * for_each_set_nbits - iterate over bitmap for each clump with set bits
+ * @start: bit offset to start search and to store the current iteration offset
+ * @clump: location to store copy of current 8-bit clump
+ * @bits: bitmap address to base the search on
+ * @size: bitmap size in number of bits
+ * @clump_size: clump size in bits
+ */
+#define for_each_set_nbits(start, clump, bits, size, clump_size) \
+	for ((start) = find_first_clump(&(clump), (bits), (size), (clump_size)); \
+	     (start) < (size); \
+	     (start) = find_next_clump(&(clump), (bits), (size), (start) + (clump_size), (clump_size)))
+
 /*
  * Return the GPIO number of the passed descriptor relative to its chip
  */
Signature · 1 line
2.29.0
#2 lore raw

PATCH RESEND v4 2/3 gpio: thunderx: Utilize for_each_set_nbits macro

In reply to Syed Nayyar Waris

This patch reimplements the thunderx_gpio_set_multiple function in drivers/gpio/gpio-thunderx.c to use the new for_each_set_nbits macro. Instead of looping for each bank in thunderx_gpio_set_multiple function, now we can skip bank which is not set and save cycles.

---
 drivers/gpio/gpio-thunderx.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)
drivers/gpio/gpio-thunderx.c +8 -5
index 9f66deab46ea..4349e7393a1d 100644
@@ -16,7 +16,7 @@
 #include <linux/pci.h>
 #include <linux/spinlock.h>
 #include <asm-generic/msi.h>
-
+#include "gpiolib.h"
 
 #define GPIO_RX_DAT	0x0
 #define GPIO_TX_SET	0x8
@@ -275,12 +275,15 @@ static void thunderx_gpio_set_multiple(struct gpio_chip *chip,
 				       unsigned long *bits)
 {
 	int bank;
-	u64 set_bits, clear_bits;
+	unsigned long set_bits, clear_bits, gpio_mask;
+	unsigned long offset;
+
 	struct thunderx_gpio *txgpio = gpiochip_get_data(chip);
 
-	for (bank = 0; bank <= chip->ngpio / 64; bank++) {
-		set_bits = bits[bank] & mask[bank];
-		clear_bits = ~bits[bank] & mask[bank];
+	for_each_set_nbits(offset, gpio_mask, mask, chip->ngpio, 64) {
+		bank = offset / 64;
+		set_bits = bits[bank] & gpio_mask;
+		clear_bits = ~bits[bank] & gpio_mask;
 		writeq(set_bits, txgpio->register_base + (bank * GPIO_2ND_BANK) + GPIO_TX_SET);
 		writeq(clear_bits, txgpio->register_base + (bank * GPIO_2ND_BANK) + GPIO_TX_CLR);
 	}
Signature · 1 line
2.29.0
#3 lore raw

PATCH RESEND v4 3/3 gpio: xilinx: Utilize generic bitmap_get_value and _set_value

In reply to Syed Nayyar Waris

This patch reimplements the xgpio_set_multiple() function in drivers/gpio/gpio-xilinx.c to use the new generic functions:
bitmap_get_value() and bitmap_set_value(). The code is now simpler to read and understand. Moreover, instead of looping for each bit in xgpio_set_multiple() function, now we can check each channel at a time and save cycles.

---
 drivers/gpio/gpio-xilinx.c | 52 +++++++++++++++++++-------------------
 1 file changed, 26 insertions(+), 26 deletions(-)
drivers/gpio/gpio-xilinx.c +26 -26
index b411d3156e0b..512198250b02 100644
@@ -18,6 +18,7 @@
 #include <linux/of_platform.h>
 #include <linux/pm_runtime.h>
 #include <linux/slab.h>
+#include "gpiolib.h"
 
 /* Register Offset Definitions */
 #define XGPIO_DATA_OFFSET   (0x0)	/* Data register  */
@@ -161,35 +162,34 @@ static void xgpio_set_multiple(struct gpio_chip *gc, unsigned long *mask,
 {
 	unsigned long flags;
 	struct xgpio_instance *chip = gpiochip_get_data(gc);
-	int index = xgpio_index(chip, 0);
-	int offset, i;
 
-	spin_lock_irqsave(&chip->gpio_lock, flags);
+	u32 *state = chip->gpio_state;
+	unsigned int *width = chip->gpio_width;
+	DECLARE_BITMAP(old, 64);
+	DECLARE_BITMAP(new, 64);
+	DECLARE_BITMAP(changed, 64);
 
-	/* Write to GPIO signals */
-	for (i = 0; i < gc->ngpio; i++) {
-		if (*mask == 0)
-			break;
-		/* Once finished with an index write it out to the register */
-		if (index !=  xgpio_index(chip, i)) {
-			xgpio_writereg(chip->regs + XGPIO_DATA_OFFSET +
-				       index * XGPIO_CHANNEL_OFFSET,
-				       chip->gpio_state[index]);
-			spin_unlock_irqrestore(&chip->gpio_lock, flags);
-			index =  xgpio_index(chip, i);
-			spin_lock_irqsave(&chip->gpio_lock, flags);
-		}
-		if (__test_and_clear_bit(i, mask)) {
-			offset =  xgpio_offset(chip, i);
-			if (test_bit(i, bits))
-				chip->gpio_state[index] |= BIT(offset);
-			else
-				chip->gpio_state[index] &= ~BIT(offset);
-		}
-	}
+	spin_lock_irqsave(&chip->gpio_lock, flags);
 
-	xgpio_writereg(chip->regs + XGPIO_DATA_OFFSET +
-		       index * XGPIO_CHANNEL_OFFSET, chip->gpio_state[index]);
+	/* Copy initial value of state bits into 'old' contiguously */
+	bitmap_set_value(old, 64, state[0], width[0], 0);
+	bitmap_set_value(old, 64, state[1], width[1], width[0]);
+	/* Copy value from 'old' into 'new' with mask applied */
+	bitmap_replace(new, old, bits, mask, gc->ngpio);
+
+	bitmap_from_arr32(old, state, 64);
+	/* Update 'state' */
+	state[0] = bitmap_get_value(new, 0, width[0]);
+	state[1] = bitmap_get_value(new, width[0], width[1]);
+	bitmap_from_arr32(new, state, 64);
+	/* XOR operation sets only changed bits */
+	bitmap_xor(changed, old, new, 64);
+
+	if (((u32 *)changed)[0])
+		xgpio_writereg(chip->regs + XGPIO_DATA_OFFSET, state[0]);
+	if (((u32 *)changed)[1])
+		xgpio_writereg(chip->regs + XGPIO_DATA_OFFSET +
+			XGPIO_CHANNEL_OFFSET, state[1]);
 
 	spin_unlock_irqrestore(&chip->gpio_lock, flags);
 }
Signature · 1 line
2.29.0
#4 lore raw

Re: [RESEND PATCH v4 3/3] gpio: xilinx: Utilize generic bitmap_get_value and _set_value

Quoted 6 lines · Syed Nayyar Waris

This patch reimplements the xgpio_set_multiple() function in drivers/gpio/gpio-xilinx.c to use the new generic functions:
bitmap_get_value() and bitmap_set_value(). The code is now simpler to read and understand. Moreover, instead of looping for each bit in xgpio_set_multiple() function, now we can check each channel at a time and save cycles.

As promised, I have looked at this with a fresh eye and NAK from me. Sorry. This is less than a half baked solution. I spent couple of evenings, so I'll come up with full conversion of this driver to the bitmap API. And yes, as I have told you like half a year before, bitmap_get_value32() and bitmap_set_value32() is much more useful (and I actually implemented them locally for the sake of conversion).

So, summarize this I do not think we have real users of the proposed API.

Signature · 2 lines
With Best Regards,
Andy Shevchenko
#5 lore raw
In reply to Syed Nayyar Waris
Quoted 9 lines · Syed Nayyar Waris

Hello Bartosz,

Since this patchset primarily affects GPIO drivers, would you like to pick it up through your GPIO tree?

This patchset introduces a new generic version of for_each_set_nbits. The previous version of for_each_set_clump8 used a fixed size 8-bit clump, but the new generic version can work with clump of any size but

clumps

Quoted 16 lines

less than or equal to BITS_PER_LONG. The patchset utilizes the new macro in several GPIO drivers.

The earlier 8-bit for_each_set_clump8 facilitated a
for-loop syntax that iterates over a memory region entire groups of set bits at a time.

For example, suppose you would like to iterate over a 32-bit integer 8 bits at a time, skipping over 8-bit groups with no set bit, where XXXXXXXX represents the current 8-bit group:

    Example:        10111110 00000000 11111111 00110011
    First loop:     10111110 00000000 11111111 XXXXXXXX
    Second loop:    10111110 00000000 XXXXXXXX 00110011
    Third loop:     XXXXXXXX 00000000 11111111 00110011
Quoted 5 lines

Each iteration of the loop returns the next 8-bit group that has at least one set bit.

But with the new for_each_set_nbits the clump size can be different from 8 bits. Moreover, the clump can be split at word boundary in situations where word

boundaries

Quoted 40 lines

size is not multiple of clump size. Following are examples showing the working of new macro for clump sizes of 24 bits and 6 bits.

Example 1:
clump size: 24 bits, Number of clumps (or ports): 10
bitmap stores the bit information from where successive clumps are retrieved.

     /* bitmap memory region */
        0x00aa0000ff000000;  /* Most significant bits */
        0xaaaaaa0000ff0000;
        0x000000aa000000aa;
        0xbbbbabcdeffedcba;  /* Least significant bits */

Different iterations of for_each_set_nbits:-
'offset' is the bit position and 'clump' is the 24 bit clump from the above bitmap.

Iteration first:        offset: 0 clump: 0xfedcba
Iteration second:       offset: 24 clump: 0xabcdef
Iteration third:        offset: 48 clump: 0xaabbbb
Iteration fourth:       offset: 96 clump: 0xaa
Iteration fifth:        offset: 144 clump: 0xff
Iteration sixth:        offset: 168 clump: 0xaaaaaa
Iteration seventh:      offset: 216 clump: 0xff

Loop breaks because in the end the remaining bits (0x00aa) size was less than clump size of 24 bits.

In above example it can be seen that in iteration third, the 24 bit clump that was retrieved was split between bitmap[0] and bitmap[1]. This example also shows that 24 bit zeroes if present in between, were skipped (preserving the previous for_each_set_macro8 behaviour).

Example 2:
clump size = 6 bits, Number of clumps (or ports) = 3.

     /* bitmap memory region */
        0x00aa0000ff000000;  /* Most significant bits */
        0xaaaaaa0000ff0000;
        0x0f00000000000000;
        0x0000000000000ac0;  /* Least significant bits */
Quoted 6 lines

Different iterations of for_each_set_nbits:
'offset' is the bit position and 'clump' is the 6 bit clump from the above bitmap.
Iteration first: offset: 6 clump: 0x2b
Loop breaks because 6 * 3 = 18 bits traversed in bitmap. Here 6 * 3 is clump size * no. of clumps.

Bart, I would like to have a fresh look at this.

(missed changelog)

Quoted 37 lines

Changes in v4:
- [Patch 3/3]: Remove extra line and add few comments.
- [Patch 3/3]: Use single lock (and unlock) call instead of two lock (and two unlock) calls.
- [Patch 3/3]: Use bitmap_from_arr32() where applicalble.
- [Patch 3/3]: Remove unnecessary 'const'.

Changes in v3:
- [Patch 1/3]: Rename for_each_set_clump to for_each_set_nbits.
- [Patch 1/3]: Shift function definitions outside 'ifdef CONFIG_DEBUG_FS' macro guard to resolve build (linking) error in xilinx Patch[3/3].
- [Patch 2/3]: Rename for_each_set_clump to for_each_set_nbits.

Changes in v2:
- [Patch 1/3]: Shift the macros and related functions to gpiolib inside gpio/. Reduce the visibilty of 'for_each_set_clump' to gpio.
- [Patch 1/3]: Remove __builtin_unreachable and simply use return statement.
- Remove tests from lib/test_bitmap.c as 'for_each_set_clump' is now localised inside gpio/ only.

Syed Nayyar Waris (3):
gpiolib: Introduce the for_each_set_nbits macro
gpio: thunderx: Utilize for_each_set_nbits macro
gpio: xilinx: Utilize generic bitmap_get_value and _set_value

 drivers/gpio/gpio-thunderx.c | 13 ++++--
 drivers/gpio/gpio-xilinx.c   | 52 ++++++++++-----------
 drivers/gpio/gpiolib.c       | 90 ++++++++++++++++++++++++++++++++++++
 drivers/gpio/gpiolib.h       | 28 +++++++++++
 4 files changed, 152 insertions(+), 31 deletions(-)

base-commit: e1b7033ecdac56c1cc4dff72d67cac25d449efc6 --
2.29.0

Signature · 2 lines
With Best Regards,
Andy Shevchenko