linux-kernel - Re: [PATCH V3 02/20] OPP: Make dev_pm_opp_set_regulators() accept NULL terminated list

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Date:   Wed, 6 Jul 2022 09:09:50 +0100
From:   Steven Price <steven.price@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Qiang Yu <yuq825@...il.com>, Rob Herring <robh@...nel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        Nishanth Menon <nm@...com>, Stephen Boyd <sboyd@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org, lima@...ts.freedesktop.org,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH V3 02/20] OPP: Make dev_pm_opp_set_regulators() accept
 NULL terminated list

On 05/07/2022 05:34, Viresh Kumar wrote:
> On 04-07-22, 15:35, Steven Price wrote:
>> I have to say the 'new improved' list ending with NULL approach doesn't
>> work out so well for Panfrost. We already have to have a separate
>> 'num_supplies' variable for devm_regulator_bulk_get() /
>> regulator_bulk_{en,dis}able(), so the keeping everything in sync
>> argument is lost here.
>>
>> I would suggest added the NULL on the end of the lists in panfrost_drv.c
>> but then it would break the use of ARRAY_SIZE() to automagically keep
>> the length correct...
> 
> Actually we can still make it work.
> 
>> For now the approach isn't too bad because Panfrost doesn't yet support
>> enabling devfreq with more than one supply. But that array isn't going
>> to work so nicely when that restriction is removed.
>>
>> The only sane way I can see of handling this in Panfrost would be
>> replicating the loop to count the supplies in the Panfrost code which
>> would allow dropping num_supplies from struct panfrost_compatible and
>> then supply_names in the same struct could be NULL terminated ready for
>> devm_pm_opp_set_regulators().
> 
> Or doing this, which will simplify both the cases.

Yes the below works, it's just a bit ugly having the "- 1", and
potentially easy to forgot when adding another. However I don't suppose
it would get far in that case so I think it would be spotted quickly
when adding a new compatible.

It's probably the best solution at the moment.

Thanks,

Steve

> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> index 7fcbc2a5b6cd..b3b55565b8ef 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> @@ -625,24 +625,29 @@ static int panfrost_remove(struct platform_device *pdev)
>         return 0;
>  }
>  
> -static const char * const default_supplies[] = { "mali" };
> +/*
> + * The OPP core wants the supply names to be NULL terminated, but we need the
> + * correct num_supplies value for regulator core. Hence, we NULL terminate here
> + * and then initialize num_supplies with ARRAY_SIZE - 1.
> + */
> +static const char * const default_supplies[] = { "mali", NULL };
>  static const struct panfrost_compatible default_data = {
> -       .num_supplies = ARRAY_SIZE(default_supplies),
> +       .num_supplies = ARRAY_SIZE(default_supplies) - 1,
>         .supply_names = default_supplies,
>         .num_pm_domains = 1, /* optional */
>         .pm_domain_names = NULL,
>  };
>  
>  static const struct panfrost_compatible amlogic_data = {
> -       .num_supplies = ARRAY_SIZE(default_supplies),
> +       .num_supplies = ARRAY_SIZE(default_supplies) - 1,
>         .supply_names = default_supplies,
>         .vendor_quirk = panfrost_gpu_amlogic_quirk,
>  };
>  
> -static const char * const mediatek_mt8183_supplies[] = { "mali", "sram" };
> +static const char * const mediatek_mt8183_supplies[] = { "mali", "sram", NULL };
>  static const char * const mediatek_mt8183_pm_domains[] = { "core0", "core1", "core2" };
>  static const struct panfrost_compatible mediatek_mt8183_data = {
> -       .num_supplies = ARRAY_SIZE(mediatek_mt8183_supplies),
> +       .num_supplies = ARRAY_SIZE(mediatek_mt8183_supplies) - 1,
>         .supply_names = mediatek_mt8183_supplies,
>         .num_pm_domains = ARRAY_SIZE(mediatek_mt8183_pm_domains),
>         .pm_domain_names = mediatek_mt8183_pm_domains,
>