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

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Date:   Tue, 5 Jul 2022 10:04:39 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Steven Price <steven.price@....com>
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 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.

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,

-- 
viresh