Computation of the clock prescaler value returned bogus results if the requested SPI clock was impossible to set. It now sets either the maximum or minimum clock frequency, as appropriate.

Signed-off-by Thomas Koeller <[email protected]>

---
 drivers/spi/davinci_spi.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)

drivers/spi/davinci_spi.c +9 -3

index 956f617..02e1a76 100644
@@ -153,7 +153,7 @@ static int davinci_spi_setup_transfer(struct spi_device *spi,
 	struct davinci_spi *davinci_spi;
 	struct davinci_spi_platform_data *pdata;
 	u8 bits_per_word = 0;
-	u32 hz = 0, prescale;
+	u32 hz = 0, prescale = 0, clkspeed;
 
 	davinci_spi = spi_master_get_devdata(spi->master);
 	pdata = davinci_spi->pdata;

@@ -190,10 +190,16 @@ static int davinci_spi_setup_transfer(struct spi_device *spi,
 	set_fmt_bits(davinci_spi->base, bits_per_word & 0x1f,
 			spi->chip_select);
 
-	prescale = ((clk_get_rate(davinci_spi->clk) / hz) - 1) & 0xff;
+	clkspeed = clk_get_rate(davinci_spi->clk);
+	if (hz > clkspeed / 2)
+		prescale = 1 << 8;
+	if (hz < clkspeed / 256)
+		prescale = 255 << 8;
+	if (!prescale)
+		prescale = ((clkspeed / hz - 1) << 8) & 0x0000ff00;
 
 	clear_fmt_bits(davinci_spi->base, 0x0000ff00, spi->chip_select);
-	set_fmt_bits(davinci_spi->base, prescale << 8, spi->chip_select);
+	set_fmt_bits(davinci_spi->base, prescale, spi->chip_select);
 
 	return 0;
 }

Signature · 4 lines

1.7.0.3


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Grant Likely

2010-04-26 15:06 UTC #5 lore raw

In reply to a message not in the archive

Quoted 26 lines · On Mon, Apr 26, 2010 at 3:01 AM, <thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ@public…

From: Thomas Koeller <[email protected]>

Computation of the clock prescaler value returned bogus results if the requested SPI clock was impossible to set. It now sets either the maximum or minimum clock frequency, as appropriate.

Signed-off-by Thomas Koeller <[email protected]>

---
drivers/spi/davinci_spi.c | 12 +++++++++---

 1 files changed, 9 insertions(+), 3 deletions(-)

drivers/spi/davinci_spi.c +1 -1

index 956f617..02e1a76 100644
@@ -153,7 +153,7 @@ static int davinci_spi_setup_transfer(struct spi_device *spi,
        struct davinci_spi *davinci_spi;
        struct davinci_spi_platform_data *pdata;
        u8 bits_per_word = 0;
-       u32 hz = 0, prescale;
+       u32 hz = 0, prescale = 0, clkspeed;
 
        davinci_spi = spi_master_get_devdata(spi->master);
        pdata = davinci_spi->pdata;

@@ -190,10 +190,16 @@ static int davinci_spi_setup_transfer(struct spi_device *spi,
        set_fmt_bits(davinci_spi->base, bits_per_word & 0x1f,

drivers/spi/davinci_spi.c static int davinci_spi_setup_transfer(struct spi_device *spi, · line 199

Quoted 10 lines

drivers/spi/davinci_spi.c +7 -1

                        spi->chip_select);
 
-       prescale = ((clk_get_rate(davinci_spi->clk) / hz) - 1) & 0xff;
+       clkspeed = clk_get_rate(davinci_spi->clk);
+       if (hz > clkspeed / 2)
+               prescale = 1 << 8;
+       if (hz < clkspeed / 256)
+               prescale = 255 << 8;
+       if (!prescale)
+               prescale = ((clkspeed / hz - 1) << 8) & 0x0000ff00;

Is be appropriate to WARN_ON() or WARN_ONCE() when the clamp condition occurs? Particularly the condition where the minimum clock speed is higher that the requested clock.

I'd also consider an if / else if / else structure for readability and clarity.

------------------------------------------------------------------------------

[email protected]

author

2010-05-31 14:33 UTC #7 lore raw

PATCH 1/1 DaVinci SPI: Fix SPI clock prescale factor computation

In reply to a message not in the archive

From: Thomas Koeller <[email protected]>

Computation of the clock prescaler value returned bogus results if the requested SPI clock was impossible to set. It now sets either the maximum or minimum clock frequency, as appropriate.

Signed-off-by Thomas Koeller <[email protected]>

---
 drivers/spi/davinci_spi.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)

drivers/spi/davinci_spi.c +0 -0

index 956f617..5c69d78 100644
@@ -153,7 +153,7 @@ static int davinci_spi_setup_transfer(struct spi_device

*spi,
struct davinci_spi *davinci_spi;
struct davinci_spi_platform_data *pdata;
u8 bits_per_word = 0;
- u32 hz = 0, prescale;
+ u32 hz = 0, prescale, clkspeed;

davinci_spi = spi_master_get_devdata(spi->master);
pdata = davinci_spi->pdata;
@@ -190,10 +190,16 @@ static int davinci_spi_setup_transfer(struct spi_device *spi,
set_fmt_bits(davinci_spi->base, bits_per_word & 0x1f,
spi->chip_select);

- prescale = ((clk_get_rate(davinci_spi->clk) / hz) - 1) & 0xff;
+ clkspeed = clk_get_rate(davinci_spi->clk);
+ if (WARN_ON(hz > clkspeed / 2))
+ prescale = 1 << 8;
+ else if (WARN_ON(hz < clkspeed / 256))
+ prescale = 255 << 8;
+ else
+ prescale = ((clkspeed / hz - 1) << 8) & 0x0000ff00;

clear_fmt_bits(davinci_spi->base, 0x0000ff00, spi->chip_select);
- set_fmt_bits(davinci_spi->base, prescale << 8, spi->chip_select);
+ set_fmt_bits(davinci_spi->base, prescale, spi->chip_select);

return 0;
}

Signature · 4 lines

1.7.0.3


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