linux-kernel - Re: [PATCH] Revert "spi: modify set_cs

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Message-ID: <bce800ff-9b3e-500b-6a42-9a60d3a0c590@collabora.com>
Date:   Thu, 30 Sep 2021 15:06:52 +0200
From:   Dafna Hirschfeld <dafna.hirschfeld@...labora.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     kernel@...labora.com, linux-spi@...r.kernel.org,
        enric.balletbo@...labora.com, dafna3@...il.com,
        Mason Zhang <Mason.Zhang@...iatek.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, wsd_upstream@...iatek.com,
        Matthias Brugger <matthias.bgg@...il.com>
Subject: Re: [PATCH] Revert "spi: modify set_cs_timing parameter"



On 30.09.21 14:46, Mark Brown wrote:
> On Thu, Sep 30, 2021 at 02:36:01PM +0200, Dafna Hirschfeld wrote:
>> hi, thanks for the fast feedback
>>
>> On 30.09.21 14:25, Mark Brown wrote:
>>> On Thu, Sep 30, 2021 at 02:07:00PM +0200, Dafna Hirschfeld wrote:
>>>> This reverts commit 04e6bb0d6bb127bac929fb35edd2dd01613c9520.
> 
>>> Which is not what the commit message nor the paste of the full hash
>>> claimed :/
> 
>> What is the paste of the full hash?
> 
> The above.
> 
>> Since the second commit is only a warning fixes I thought it is cumbersome to
>> send two separate reverting patches. Should I?
> 
> No, you should write a proper commit log with (like I said) a normal
> subject line - basically, follow the process in submitting-patches.rst.
> 
>>> Do we have any analysis as to why?  Do these devices use timing
>>> parameters in some way for example, or do the values written out to the
>>> device change in some way?
> 
>>> You've provided no analysis here so it's hard to tell if this is just
>>> some random change that happens to change code generation slighly or if
>>> there's some actual reason why this might fix something.  I'll note that
>>> as far as I can see there are no users of this API upstream so I'm
>>> guessing that you've got some out of tree consumer driver which uses the
>>> API, it's possible that there was some error in updating that driver to
>>> the new interface which is causing the issue.
> 
>> Actually the original commit not only change that callback 'set_cs_timing' but it also
>> calls 'mtk_spi_set_hw_cs_timing' directly from the function "mtk_spi_prepare_message".
>> So this actually influences all devices bound to this driver (in upstream)
>> I did some printing and it does change values that are written to registers.
> 
> OK, so that's something that should have been in the commit log,
> preferrably in a more detailed form that identifies what the change is.
> However changing the values written out is clearly not the intent of the
> patch and it is a substantially better API so can we not just fix things
> so that the old values are written out?  Why are we jumping straight to
> a revert here?

It could be that the values written to the register in the new version of "mtk_spi_set_hw_cs_timing" are the same
as with the previous version. I didn't check that. The difference is that before that patch
the function was not called so it was a dead code. Now it is called and causes erros.
Without the datasheet it is hard to know how to fix it. I responded to that patch two days ago explaining
that but Mason Zhang didn't respond yet.

Thanks,
Dafna

>