[U-Boot] [PATCH v2] dm: spi: prevent setting a speed of 0 Hz

[Simon Goldschmidt]

[Responding from my work address due to problems with gmail]

On 23.11.2018 13:27, Jagan Teki wrote:
> On Fri, Nov 23, 2018 at 1:51 AM <sjg at google.com> wrote:
>>
>> On Fri, 16 Nov 2018 at 12:40, Simon Goldschmidt
>> <simon.k.r.goldschmidt at gmail.com> wrote:
>>>
>>> On 31.10.2018 07:42, Simon Goldschmidt wrote:
>>>> On Wed, Oct 31, 2018 at 7:22 AM Jagan Teki <jagan at amarulasolutions.com> wrote:
>>>>> On Wed, Oct 31, 2018 at 1:40 AM Simon Goldschmidt
>>>>> <simon.k.r.goldschmidt at gmail.com> wrote:
>>>>>> When the device tree is missing a correct spi slave description below
>>>>>> the bus (compatible "spi-flash" or spi-max-frequency are missing),
>>>>>> the 'set_speed' callback can be called with 'speed' == 0 Hz.
>>>>>> At least with cadence qspi, this leads to a division by zero.
>>>>>>
>>>>>> Prevent this by initializing speed to 100 kHz in this case (same
>>>>>> fallback value as is done in 'dm_spi_claim_bus') and issue a warning
>>>>>> to console.
>>>>> Why can't driver plat->frequency in cadence driver initialize 100KH?
>>>>> plat->frequency = fdtdec_get_int(blob, node, "spi-max-frequency", 100000)
>>>> I'm not sure I understand.
>>>> The cadence driver initializes its 'plat->max_hz' from
>>>> "spi-max-frequency" property and defaults to 500 kHz. No problem
>>>> there.
>>>>
>>>> However, the problem I want to solve is if someone puts a flash chip
>>>> below there which has compatible != "spi-flash", they will get a hard
>>>> fault which is hard to debug. This is because the node is not parsed
>>>> because of the wrong compatible string (even if there is an
>>>> "spi-max-frequency" property) and thus, "sf probe" tries to continue
>>>> with 0 Hz.
>>>>
>>>> And this can happen easily when porting device trees from Linux as
>>>> there, the boards have compatible "n25q00" etc. instead of
>>>> "spi-flash", which is U-Boot specific (sadly).
>>>>
>>>> This patch is not required to make valid U-Boot devicetrees work, it
>>>> is meant to get better error handling for devicetrees ported from
>>>> Linux.
>>>>
>>>> An even better fix would be for U-Boot not to require the compatible =
>>>> "spi-flash" string but just work correctly with Linux device trees,
>>>> but that's not within my possibilities right now :-(
>>>
>>> Ping? This is a bug that should hit nearly everyone porting a board dts
>>> working in Linux to U-Boot, can we please have some kind of fix for this?
>>> Currently, using a dts with an spi flash chip that works in Linux may
>>> abort in U-Boot...
>>
>> Reviewed-by: Simon Glass <sjg at chromium.org>
>>
>> Applied to u-boot-dm/master, thanks!
> 
> I hold this because, there is a discussion going on with me and
> Simon.k about Linux compatible "jedec,spi-nor".  adding support for
> this binding would eventually not reproduce this issue.

That's not completely true. Adding "jedec,spi-nor" to U-Boot would
definitively make it less likely to run into this issue.

However, Linux works correctly without "jedec,spi-nor", so people can
still run into problems when porting a dts from Linux. This is why I
still would like to get this in.


Simon