[U-Boot] [EXT] Re: [PATCH 1/6] spi: fsl_qspi: Fix DDR mode setting for latest iMX platforms

[Schrempf Frieder]

Hi Stefan,

On 22.10.19 15:18, Stefan Roese wrote:
> Hi Frieder,
> Hi Ashish,
> Hi Ye Li,
> Hi Fabio,
> 
> On 18.09.19 09:42, Stefan Roese wrote:
>> Hi Frieder,
>>
>> On 18.09.19 09:08, Schrempf Frieder wrote:
>>
>> <snip>
>>
>>>> One further update on this QSPI driver. This driver only works when
>>>> loaded via "imx_usb" on the i.MX6ULL EVK. When programmed into QSPI
>>>> and booted from QSPI this driver does not detect the SPI NOR
>>>> flash:
>>>>
>>>> => sf probe
>>>> unrecognized JEDEC id bytes: ff, ff, ff
>>>>
>>>> Do you have any idea what might explain this difference. I would have
>>>> expected that when booting via QSPI it would be "easier" for the
>>>> driver, as the BootROM already initializes the QSPI interface. Which
>>>> is not the case in the boot via serial download (imx_usb) mode. Here
>>>> everyhting (pinmux, clocks, etc) need to be configured.
>>>>
>>>> My feeling is that something is configured "incorrectly" by the
>>>> BootROM in this case which is not re-configured as the QSPI driver
>>>> needs it to be currently.
>>>>
>>>> Do you have any ideas on what might be the problem here? Is there
>>>> something that I can do to help test this? Would it help if I would
>>>> send the debug logging of the driver?
>>>
>>> I have a strong suspicion of what goes wrong in your case. We
>>> experienced exactly the same issue recently on i.MX6ULL. For some
>>> reasons (I guess differences in BootROM) this does not happen on 
>>> i.MX6UL.
>>>
>>> The problem is, that the BootROM sets the TDH bits in the QuadSPI_FLSHCR
>>> register to '01' in case it uses the DDR mode. Afterwards when U-Boot or
>>> Linux try to access the flash in SDR mode, they fail as the TDH bits are
>>> still set. Resetting them to '00' solves the problem.
>>>
>>> Unfortunately the TDH bits are not documented in the manual of the
>>> i.MX6UL/ULL, but they can be found in the manual of the i.MX7.
>>>
>>> For the QSPI driver, this means it needs a fix to set/reset the TDH bits
>>> according to the mode that is used (DDR/SDR).
>>>
>>> For more details please also look here:
>>> https://community.nxp.com/thread/507260
>>
>> Perfect. With these bits set to 00 again, booting from QSPI now
>> works on the EVK. Many thanks for this hint! :)
> 
> I'm coming back to this issue, as we now have the new NXP patches
> integrated into mainline. Including this one:
> 
> 7949576664ac "spi: fsl_qspi: Fix DDR mode setting for latest iMX platforms" >
> I've now re-tested current mainline on the i.MX6ULL Eval Kit and QSPI
> does not work reliably. This is with CONFIG_SYS_FSL_QSPI_AHB enabled
> and disabled. How is QSPI supposed to work on i.MX6ULL/ULZ? Is any
> one of you running this current mainline driver successfully on one
> any i-MX6ULL/ULZ based board? If yes, what is your configuration here?

I don't have any experience with the current mainline SPI NOR driver.

> 
> BTW: Using the "spi-mem" driver version from Ashish with the fix
> suggested by Frieder to clear the DDR bit in TDH (reset to 00) still
> works without any problems.

There is some cleanup work that needs to be done (e.g. [1]). After that 
I will send an official patch for the spi-mem driver. Then Ashish and 
you can comment with your test results and change requests.

I have also sent a fix for the TDH bit for the Linux driver [2]. This is 
also applicable to the new U-Boot driver.

Regards,
Frieder

[1]: https://github.com/fschrempf/u-boot/commits/spi_flash_kconfig_cleanup
[2]: https://patchwork.kernel.org/patch/11176905/