Re: [PATCH] Revert "spi: modify set_cs_timing parameter"

From: Mark Brown <broonie@kernel.org>
To: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
Cc: kernel@collabora.com, linux-spi@vger.kernel.org,
	enric.balletbo@collabora.com, dafna3@gmail.com,
	Mason Zhang <Mason.Zhang@mediatek.com>,
	Laxman Dewangan <ldewangan@nvidia.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org, wsd_upstream@mediatek.com,
	Matthias Brugger <matthias.bgg@gmail.com>
Subject: Re: [PATCH] Revert "spi: modify set_cs_timing parameter"
Date: Thu, 30 Sep 2021 13:46:30 +0100	[thread overview]
Message-ID: <20210930124630.GY4199@sirena.org.uk> (raw)
In-Reply-To: <28f8af42-4535-ef9f-e521-712d37e2cb72@collabora.com>

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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?

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