linux-kernel - Re: [PATCH v4 07/47] soc: fsl: qe: qe.c: guard use of pvr_version_is() with CONFIG

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Date:   Fri, 15 Nov 2019 09:11:41 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Timur Tabi <timur@...nel.org>
Cc:     Qiang Zhao <qiang.zhao@....com>, Li Yang <leoyang.li@....com>,
        Christophe Leroy <christophe.leroy@....fr>,
        Scott Wood <oss@...error.net>, linuxppc-dev@...ts.ozlabs.org,
        lkml <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 07/47] soc: fsl: qe: qe.c: guard use of
 pvr_version_is() with CONFIG_PPC32

On 15/11/2019 05.50, Timur Tabi wrote:
> On Fri, Nov 8, 2019 at 7:04 AM Rasmus Villemoes
> <linux@...musvillemoes.dk> wrote:
>>
>> +static bool qe_general4_errata(void)
>> +{
>> +#ifdef CONFIG_PPC32
>> +       return pvr_version_is(PVR_VER_836x) || pvr_version_is(PVR_VER_832x);
>> +#endif
>> +       return false;
>> +}
>> +
>>  /* Program the BRG to the given sampling rate and multiplier
>>   *
>>   * @brg: the BRG, QE_BRG1 - QE_BRG16
>> @@ -223,7 +231,7 @@ int qe_setbrg(enum qe_clock brg, unsigned int rate, unsigned int multiplier)
>>         /* Errata QE_General4, which affects some MPC832x and MPC836x SOCs, says
>>            that the BRG divisor must be even if you're not using divide-by-16
>>            mode. */
> 
> Can you also move this comment (and fix the comment formatting so that
> it's a proper function comment) to qe_general4_errata()?
> 

I actually thought of doing that, but decided against it because the
comment not only mentions the SOCs affected, but also explains the
following math/logic. I mean, without that comment nearby, the code is

  if (qe_general4_errata())
     if (some weird condition)
        divisor++;

In contrast, I think the qe_general4_errata() is pretty self-explanatory
- is this a SOC affected by that errata (whatever that errata may be
about and what the software workaround is).

Rasmus