linux-kernel - Re: [PATCH 01/33] clk_ops: change round

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Date:   Tue, 2 Jan 2018 20:43:44 +0000
From:   Bryan O'Donoghue <pure.logic@...us-software.ie>
To:     Stephen Boyd <sboyd@...eaurora.org>
Cc:     Mikko Perttunen <cyndis@...si.fi>, mturquette@...libre.com,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mips@...ux-mips.org, linux-rpi-kernel@...ts.infradead.org,
        patches@...nsource.cirrus.com,
        uclinux-h8-devel@...ts.sourceforge.jp,
        linux-amlogic@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
        linux-soc@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-rockchip@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-tegra@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        linux-mediatek@...ts.infradead.org,
        freedreno@...ts.freedesktop.org, linux-media@...r.kernel.org,
        linux-rtc@...r.kernel.org
Subject: Re: [PATCH 01/33] clk_ops: change round_rate() to return unsigned
 long

On 02/01/18 19:01, Stephen Boyd wrote:
> On 12/31, Bryan O'Donoghue wrote:
>> On 30/12/17 16:36, Mikko Perttunen wrote:
>>> FWIW, we had this problem some years ago with the Tegra CPU clock
>>> - then it was determined that a simpler solution was to have the
>>> determine_rate callback support unsigned long rates - so clock
>>> drivers that need to return rates higher than 2^31 can instead
>>> implement the determine_rate callback. That is what's currently
>>> implemented.
>>>
>>> Mikko
>>
>> Granted we could work around it but, having both zero and less than
>> zero indicate error means you can't support larger than LONG_MAX
>> which is I think worth fixing.
>>
> 
> Ok. But can you implement the determine_rate op instead of the
> round_rate op for your clk?

Don't know .

> It's not a work-around, it's the
> preferred solution. That would allow rates larger than 2^31 for
> the clk without pushing through a change to all the drivers to
> express zero as "error" and non-zero as the rounded rate.
> 
> I'm not entirely opposed to this approach, because we probably
> don't care to pass the particular error value from a clk provider
> to a clk consumer about what the error is.

Which was my thought. The return value of clk_ops->round_rate() appears 
not to get pushed up the stack, which is what the last patch in this 
series deals with.

[PATCH 33/33] clk: change handling of round_rate() such that only zero 
is an error

> It's actually what we
> proposed as the solution for clk_round_rate() to return values
> larger than LONG_MAX to consumers. But doing that consumer API
> change or this provider side change is going to require us to
> evaluate all the consumers of these clks to make sure they don't
> check for some error value that's less than zero. This series
> does half the work,

Do you mean users of clk_rounda_rate() ? I have a set of patches for 
that but wanted to separate that from clk_ops->round_rate() so as not to 
send ~70 patches out to LKML at once - even if they are in two blocks.

If so, I can publish that set too for reference.

AFAICT on clk_ops->round_rate the last patch #33 ought to cover the 
usage of the return value of clk_ops->round_rate().

Have I missed something ?

> by changing the provider side, while ignoring
> the consumer side and any potential fallout of the less than zero
> to zero return value change.
> 

Can you look at #33 ? I'm not sure if you saw that one.


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bod