linux-kernel - Re: [PATCH v3 0/2] mark spi clocks as critical and enable spi3 clocks

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Message-ID: <CA+Ln22HKo2kP8XXdBNve8aX8d9A1rZg7A78x+-S255Xi4k-nxg@mail.gmail.com>
Date:	Mon, 4 Jul 2016 13:55:37 +0900
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Andi Shyti <andi.shyti@...sung.com>
Cc:	Chanwoo Choi <cw00.choi@...sung.com>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Kukjin Kim <kgene@...nel.org>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>, linux-clk@...r.kernel.org,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andi Shyti <andi@...zian.org>
Subject: Re: [PATCH v3 0/2] mark spi clocks as critical and enable spi3 clocks

2016-07-04 13:20 GMT+09:00 Andi Shyti <andi.shyti@...sung.com>:
> Hi Tomasz,
>
>> > This patchset enables spi3 clocks by marking critical clocks as
>> > CLK_IS_CRITICAL and in the meantime replaces the use of
>> > CLK_IGNORE_UNUSED for spi1 clocks.
>> >
>> > The sclk needs to be considered critical as well.
>> >
>> > The SPI3 in the tm2/tm2e boards will control an irled for remote
>> > controlling.
>> >
>> > Changelog:
>> >
>> > V1 -> V2
>> >  - the "sclk_spi3" doesn't need to be enabled in boot time as it
>> >   is handled by the spi driver itself.
>> >
>> >  - use the CLK_IS_CRITICAL flag for the ioclk
>> >
>> > V2 -> V3
>> >  - some more tests has confirmed taht "sclk_spi1,3" need to be
>> >    enabled as critical!
>>
>> This sounds like a DTS and/or SPI and/or clock driver bug then. I'm
>> pretty much convinced that it might also cause other problems and this
>> workaround will only mask them making things even more difficult to
>> debug in the future. Let's not introduce more technical debt.
>
> In principle I agree, but, the upcoming TM2/TM2e boards will have
> the audio codec connected on SPI1 and the ir remote controller on
> the SPI3 (others SPI slots are used as well, but we don't have
> the drivers ready for them).
>
> I followed for SPI3 the same approach as it was done for SPI1, so
> that I see two choices here:
>
>  * reject this patches and cleanup the SPI1 from the "technical
>    debt" and not have anything working on spi.

>
> or
>
>  * do for SPI3 the same as it has been done for SPI1 (and as it
>    is now) with its "technical debt".
>
> I did quite an extensive testing on these lines and I don't see
> any other alternative.

The SPI driver is supposed to enable the SPI bus clock whenever
necessary, if it's given the clock correctly and the clock driver has
the clock hierarchy correctly defined. So I see third choice here:

 * Debug why the SPI driver doesn't properly enable the clock, fix the
cause (fixing both SPI1 and SPI3 sclk at the same time) and then
remove the CLK_IGNORE_UNUSED flag from sclk_spi1.

Of course the above doesn't apply to sclk_ioclk clocks, as we already
agreed that they need CLK_IS_CRITICAL due to their nature.

Best regards,
Tomasz