linux-kernel - Re: [PATCH 2/2] clk: pxa: fix pxa2xx_determine

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Date:   Tue, 08 Nov 2016 19:01:57 +0100
From:   Robert Jarzmik <robert.jarzmik@...e.fr>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Stephen Boyd <sboyd@...eaurora.org>,
        Michael Turquette <mturquette@...libre.com>,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] clk: pxa: fix pxa2xx_determine_rate return

Arnd Bergmann <arnd@...db.de> writes:

> The new pxa2xx_determine_rate() function seems lacking in a few
> regards:
>
> - For an exact match or no match at all, the rate is uninitialized
>   as reported by gcc -Wmaybe-unintialized:
>    drivers/clk/pxa/clk-pxa.c: In function 'pxa2xx_determine_rate':
>    drivers/clk/pxa/clk-pxa.c:243:5: error: 'rate' may be used uninitialized in
>   this function
Euh I don't think that is true.

For an exact match, rate is assigned the exact value in the first line after the
for(xxx).

For no match at all, there are 2 cases :
 - either a closest match is found, and rate is actually assigned (see below)
 - or no match is found, and it's true rate remains uninitialized, but we have
   ret = -EINVAL

> - If we get a non-exact match, the req->rate output is never set
>   to the actual rate but remains at the requested rate.
Euh no, that doesn't seem correct to me.

If a non-exact match is found, either by closest_below or closest_above, rate is
set (rate = freqs[closest_xxx].cpll). And a couple of lines later after the
if/else, req->rate = rate is set as well, so I don't think this part of the
commit message is accurate.

> - We should not attempt to print a rate if none could be found
True.

> This rewrites the logic accordingly.
Unless I'm wrong in the analysis above, I'd rather have just "unsigned long rate
= 0" in the variable declaration, and keep the pr_debug() even if -EINVAL is
returned (it's better for bug tracking, with a rate == 0 in this case for example).

Cheers.

--
Robert