[U-Boot] [PATCH 00/18] sf: fix support of QSPI memories and controllers

[Cyrille Pitchen]

Le 15/03/2016 19:21, Jagan Teki a écrit :
> On Tuesday 15 March 2016 11:42 PM, Cyrille Pitchen wrote:
>> 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
>>    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
> 
> 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 */
+	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);


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.

Best regards,

Cyrille


[1] http://lists.infradead.org/pipermail/linux-mtd/2016-February/065371.html