sf: fix support of QSPI memories and controllers

Hi Cyrille,

Quoted 253 lines · Cyrille Pitchen

Hi Stefan,

Le 18/03/2016 14:48, Stefan Roese a ?crit :

Quoted 240 lines

Hi All,

please excuse the late reply to this thread. But I'm very interested in QSPI, as one of my customers uses Micron QSPI NOR and really wants to take full advantage of the device (quad access) to speed up the overall boot process. This is on SoCFPGA btw.

Please allow me a few comments below.

Quoted 197 lines · Jagan Teki

Quoted 196 lines · Cyrille Pitchen

Le 15/03/2016 19:21, Jagan Teki a ?crit :

Quoted 38 lines · Cyrille Pitchen

Quoted 28 lines

Hi all,

This series of patches fixes and extend the support of QSPI memories in the SPI flash framework. The updates are split into many parts to make it easier to understand and review but they should be considered as a whole.

This was tested on a Atmel sama5d2 xplained board with a Micron n25q128a
memory.

Best regards,

Cyrille

Cyrille Pitchen (18):
Revert "sf: Fix quad bit set for micron devices"
sf: call spi_claim_bus() and spi_release_bus() only once per read,
write or erase
sf: replace spi_flash_read_common() calls by spi_flash_cmd_read()
sf: remove spi_flash_write_common()
sf: export spi_flash_wait_ready() function
sf: share erase generic algorithm
sf: share write generic algorithm
sf: share read generic algorithm
sf: add hooks to handle register read and write operations
sf: move support of SST flash into generic spi_flash_write_alg()
sf: fix selection of supported READ commands for QSPI memories

Quoted 8 lines

sf: fix detection of QSPI memories when they boot in Quad or
Dual mode
sf: add helper function to set the number of dummy bytes
sf: add 4byte address opcodes
sf: prepare next fixes to support of QSPI memories by manufacturer
sf: fix support of Micron memories
ARM: at91: clock: add function to get QSPI clocks
sf: add driver for Atmel QSPI controller

Quoted 8 lines

Appreciate for the work, we're working on spi-nor framework[1] planning to push in couple of weeks. Will let you know once it merged so that you can add your changes on top of that.

[1]
http://git.denx.de/?p=u-boot/u-boot-spi.git;a=shortlog;h=refs/heads/spi-nor-next

Hi Jagan,

I've started to have a look on your branch. I hope it's not to late for few
comments:

Globally I see the new code attend to match the spi-nor framework from Linux.
OK that's fine but please note the current spi-nor framework in Linux has incomplete and sometime not working support of QSPI memories.

First, after a discussion with Brian and Bean on linux-mtd [1], Bean's commit
to add support to Micron QSPI memories was reverted since it didn't work alone.
In his reply, Brian agreed the code was not tested and should not have been
merged.

This highlights a more general issue: currently, there is no mean for the spi-nor framework to notify the SPI controller driver about a SPI protocol
change at the QSPI memory side. This applies to Micron memories when they enter
their Quad I/O mode. If so, ALL commands, even JEDEC Read ID, Read Status Register, ..., MUST use the SPI 4-4-4 protocol. Commands sent using SPI 1-x-y
protocols are no longer decoded properly.
This also applies to Macronix and Winbond memories if they enter their QPI
mode, which is the equivalent of Micron Quad I/O mode.
This is why I've suggested to add 4 new fields in the struct spi_nor:
- .reg_proto: the SPI protocol to be used by .read_reg() and .write_reg() hooks.
- .read_proto: the SPI protocol to be used by the .read() hooks, maybe by the
.read_mmap() also.
- .write_proto: the SPI protocol to be used by the .write() hooks
- .erase_proto: the SPI protocol to be used by the .erase() hooks.

(Q)SPI controller drivers cannot guess the protocol to be used from the command
op code. Indeed, taking the Micron case as un example, the very same 0xeb op
code may be used with the SPI 1-4-4 protocol (Micron Extended SPI mode) or
with the SPI 4-4-4 protocol (Micron Quad I/O mode).

Also just some words about the naming of SPI x-y-z protocols:
- x refers to the number of I/O lines used to send the op code byte
- y is the number of I/O lines used to send the address, mode/dummy cycles
(if these cycles exist for the command op code)
- z is the number of I/O lines used to send/receive data (if needed)

So the SNOR_OP_READ_1_1_2_IO macro for the Fast Read Dual I/O command (as opposed to the macro SNOR_OP_READ_1_1_2 macro for the Fast Read Dual Output
command) doesn't make sense: it should be named SNOR_OP_READ_1_2_2.

Then about the value used for the dummy cycles, it's not always true that we
don't care about initializing them. Depending on the configuration of the memory, some special dummy cycles, sometime called mode cycles, are used to
during Fast Read operations to make the memory enter/leaver its Continuous Read
mode. Once is Continuous Read mode, the op code byte is no longer sent, it is
implicit and the command actually starts from the address cycles. This mode
is mostly used for XIP applications hence is not relevant for mtd usage. However we should take care not to enter this Continuous Mode by mistake. Depending on the memory manufacturer, the Continuous Mode can be disabled by
updating the relevant bit in some configuration register (e.g. setting the XIP
bit in Micron Volatile Configuration Register) or by choosing the right op code
(e.g. for Winbond memories in QPI mode, both the 0x0b and 0xeb op codes can
be used for Fast Read 4-4-4 operation but only the 0xeb op code cares about
the dummy cycle value to enter/leave the Continuous Read mode). Some Spansion memories use 6 dummy cycles for Fast Read 1-4-4 command as factory default, not 8.

Besides when sending a regular JEDEC Read ID (0x9f) command to probe the (Q)SPI
memory, the current spi-nor framework assumes the Quad I/O or QPI mode is not
already enabled. This not always true, some early bootloarders, such as the
sama5d2 ROM Code, enables the Micron Quad I/O mode when configured to boot from
the QSPI memory. If so, the QSPI memory no longer replies to the 0x9f command
in SPI 1-1-1 protocol but instead to the 0xaf command in SPI 4-4-4 protocol.

Finally, about the proper way to describe the SPI controller capabilities,
the SPI_TX_{DUAL, QUAD} and SPI_RX_{DUAL, QUAD} mode flags are set in the SPI framework based on the "spi-rx-bus-width" and "spi-tx-bus-width" DT properties already used in Linux.
This is not enough to make the difference between the SPI 1-4-4 and SPI 4-4-4
protocols. Maybe some SPI controllers support the first protocol but not the
latest. It could be good to add another argument to spi_nor_scan() providing
an exhaustive list of SPI protocols supported by the SPI controller. Then to match this list with the list of SPI protocols supported by the SPI
memory and select the proper protocol, this new argument should use the same
range of values as the .flash_read field in the struct spi_nor_info used to
describe the SPI memories.

For backward compatibility, the m25p80 driver could then convert the SPI modes
into spi-nor read modes. Please have a look at patch 11 of my series; the chunk related to spi_flash_probe_slave() in sf_probe.c:

    /* Convert SPI mode_rx and mode to SPI flash read commands */

(quoted diff) +16 -1

+    mode_rx = spi->mode_rx;
+    if (mode_rx & SPI_RX_QUAD) {
+        e_rd_cmd = RD_NORM | QUAD_OUTPUT_FAST;
+        if (spi->mode & SPI_TX_QUAD)
+            e_rd_cmd |= QUAD_IO_FAST;
+    } else if (mode_rx & SPI_RX_DUAL) {
+        e_rd_cmd = RD_NORM | DUAL_OUTPUT_FAST;
+        if (spi->mode & SPI_TX_DUAL)
+            e_rd_cmd |= DUAL_IO_FAST;
+    } else if ((mode_rx & (SPI_RX_SLOW | SPI_RX_FAST)) == SPI_RX_SLOW) {
+        e_rd_cmd = ARRAY_SLOW;
+    } else {
+        e_rd_cmd = RD_NORM;
+    }
+
[...]
-    ret = spi_flash_scan(flash);
+    ret = spi_flash_scan(flash, e_rd_cmd);

Quoted 6 lines

Quoted 6 lines

I've spent a lot of time working on the QSPI memory topic so I can tell you
that there are many other traps to avoid!
If I can help you on this topic during your rework of the SPI NOR support,
please let me know.

Thanks Cyrille, for this very detailed and good explanation. This is really appreciated. And I really hope that Jagan will get back to your generous offer, to assist with any such QSPI NOR related problems. I'll definitely remember this and might bug you at some time... ;)

Quoted 8 lines

I understand your points, thanks for that and anyway this spi-nor work is a starting point for both syncing with Linux as well with new feature or for better tunning. And more over I started this work in 2014 end and it's been reviewing over and over and we finally landed up with MTD driver model.

So, please wait for sometime until this gets merged we definitely work together for better tunning, thanks!

Jagan, what is the current plan here? I have to admit that I didn't check closely on your SPI-NOR work lately, sorry. So I can't really comment with a profound deep knowledge. But from what I read in Cyrille's patchset and explanation above, his patchset fixes some issues and brings us also more in line with the (upcoming) Linux framework. So I would really love to see this integrated into mainline quickly. Allowing a broader test basis on multiple platforms. Will it be a big task for Cyrille to rebase his patchset on top of your patches? Can you perhaps assist Cyrille with this? Or would it perhaps make sense to postpone your patchset and integrate Cyrille's first instead?

Quoted 4 lines

Cyrille, if Jagans rework goes in first, do you already have a plan on when to rebase your patchset on top of this? Or do you see some "show-stoppers" here?

Well if I need to rebase my patchset, for sure I will wait for Jagan's rework to be completed and accepted first. I don't think it would be efficient to rebase the QSPI series on the fly before the rework is totally stabilized.

Quoted 6 lines

One of the commit message from u-boot-spi.git can sum up the global rework:
"sf: Drop entire spi-flash framework" [1]

Indeed all files from drivers/mtd/spi are deleted, the next commits replace them by new files in the spi-nor folder. These new files are almost some "copy/paste" of drivers/mtd/spi-nor files from Linux.

Yeah.. the idea of using Linux spi-nor is like u-boot also facing similar issue where Linux facing like spi drivers became more flash centric, and it's not totally same design as Linux. We took the idea from Linux and have MTD driver model on top of it. The whole idea to add this is to follow the u-boot driver model principle and if the stack look some how similar to Linux then the development is as faster as, when
compared to maintain separate thread of development - this is very legacy story I have been saying on this on ML for year back.

And did you find any issues with this spi-nor series?

Quoted 6 lines

OK, why not but it also implies that I can't simply rebase my patchset. Since the all files are different it means I have to write a new series of patches from scratch. As I said, I won't start such a work before the new framework is totally accepted and integrated in next releases of u-boot.

Quoted 14 lines

I don't say using the Linux code as a reference is a bad idea, indeed there are good things in the spi-nor framework to be taken. For instance, in my own series I added .read_reg() and .write_reg() hooks the same way as done in the Linux source.
I just warn developers that currently the Linux code misses some stuff to support QSPI memories efficiently. As an example, spi_nor_scan() fails to read the JEDEC ID if the QSPI memory is already in QPI mode (Micron, Macronix, Winbond, ...).
This issue didn't exist with regular SPI NOR flash memories as they are almost "stateless" as compared to QSPI memories. SPI memories always use a single protocol, SPI 1-1-1 with MISO and MOSI I/O lines, for all commands. On the other hand, QSPI memories are much complex: you have to deal with many different protocols and find a way to guess the current internal state of the QSPI memory before sending commands to it.

OK, I understand that you sent separate patches, are these patches fix this issue?

https://patchwork.ozlabs.org/patch/598527/
https://patchwork.ozlabs.org/patch/598528/
https://patchwork.ozlabs.org/patch/598530/

https://patchwork.ozlabs.org/patch/598532/

If so, then I will start reviewing these and will push these changes first and will rebase spi-nor on top of this.

thanks!