Messages in this thread Patch in this message | | | From | Martin Blumenstingl <> | Subject | [PATCH RFC] soc: amlogic: meson-ee-pwrc: Drop the .shutdown callback from the driver | Date | Thu, 29 Apr 2021 22:37:23 +0200 |
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Stefan reports that rebooting his ODROID-N2+ (using a G12B SoC) results in the board hanging. His kernel config uses: CONFIG_MESON_EE_PM_DOMAINS=y CONFIG_DRM_MESON=m
He reports that his kernel config results in the DRM driver's .shutdown callback to be executed after the power domain driver's .shutdown callback. That's problematic because meson_ee_pwrc_shutdown disables the clock which are used by the VPU IP. This causes the board to hang.
Further he reports that changing from CONFIG_DRM_MESON=m to CONFIG_DRM_MESON=y reverses the order in which the DRM and power domain driver's shutdown functions are executed, making the reboot successful.
The reason why we use meson_ee_pwrc_shutdown is because of the VPU power domain (which is causing the problem described above). It can be left enabled by u-boot. According to the original TOFIX comment in meson_ee_pwrc_init_domain we need to be careful because disabling the power domain could "cause system errors". As a workaround the clocks are manually enabled in meson_ee_pwrc_init_domain and the power domain is marked as GENPD_FLAG_ALWAYS_ON (so it can never be turned off).
Experimenting has shown that the power domain itself can be disabled as long as we keep the clocks enabled if u-boot enabled the power domain but we don't have any driver enabled for the VPU (CONFIG_DRM_MESON=n).
Keeping the clocks enabled is the responsibility of the CCF drivers, not the power domain driver. Even better: this is already covered as all gates in the VPU and VAPB tree on GX an G12 SoCs have the CLK_IGNORE_UNUSED flag set, meaning: if the bootloader has previously enabled the clock we're not touching it until a driver explicitly asks to enable (and then disable) it. In case of CONFIG_DRM_MESON=n we're never calling meson_ee_pwrc_on, meaning that we always keep the state of the clocks as set by u-boot.
The original TOFIX comment also mentioned that we need to make sure not to mess up the clock's prepare/enable ref-counters. This is the only requirement that's left for the meson-ee-pwrc driver that needs to be managed for the VPU power domain.
Three steps can improve this situation: - Don't prepare and enable the clocks (just to fix the ref-counting) in meson_ee_pwrc_init_domain if u-boot left that power domain enabled. Instead, remember if the clocks are enabled in meson_ee_pwrc_{on,off} and only disable them if we have previously turned them on ourselves. - Drop GENPD_FLAG_ALWAYS_ON as we can always manage the state of the VPU power domain if both the power domain controller and DRM driver are enabled (=m or =y). If the power domain driver is enabled but the DRM driver is disabled we can still use meson_ee_pwrc_off because it's not trying to disable the clocks anymore - Drop meson_ee_pwrc_shutdown as it's the responsibility of the genpd framework to call meson_ee_pwrc_off when needed (either when a power domain is being disabled - regardless of whether it's was used by a driver before or not). Now there's also no more shutdown callback ordering dependency between the power domain driver and other drivers anymore.
Fixes: eef3c2ba0a42a6 ("soc: amlogic: Add support for Everything-Else power domains controller") Reported-by: Stefan Agner <stefan@agner.ch> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com> --- Neil, I would like you to specifically review (and re-test) the original TOFIX part. I *believe* that I understand the original problem and hope that my approach also works in that scenario, but I am not 100% sure.
Kevin, as you're my go-to genpd expert I am also asking you to review this to point out any issues you see.
drivers/soc/amlogic/meson-ee-pwrc.c | 76 ++++++++++++----------------- 1 file changed, 31 insertions(+), 45 deletions(-)
diff --git a/drivers/soc/amlogic/meson-ee-pwrc.c b/drivers/soc/amlogic/meson-ee-pwrc.c index 50bf5d2b828b..534c33ba31ce 100644 --- a/drivers/soc/amlogic/meson-ee-pwrc.c +++ b/drivers/soc/amlogic/meson-ee-pwrc.c @@ -353,10 +353,26 @@ static int meson_ee_pwrc_off(struct generic_pm_domain *domain) if (pwrc_domain->num_clks) { msleep(20); - clk_bulk_disable_unprepare(pwrc_domain->num_clks, - pwrc_domain->clks); + + /* + * We are only allowed to turn off the clocks here if we + * have previously enabled them ourselves. In other words: + * for an "unused" power domain (which is not used by any + * power domain consumer) we have not enabled the clocks + * previously so we keep them in the state they are. + * This is relevant for the VPU power domain which may + * have been enabled by u-boot. If the display driver in + * Linux is disabled then we need to keep the clocks in + * the state as u-boot set them, otherwise the board will + * hang. + */ + if (pwrc_domain->enabled) + clk_bulk_disable_unprepare(pwrc_domain->num_clks, + pwrc_domain->clks); } + pwrc_domain->enabled = false; + return 0; } @@ -392,8 +408,14 @@ static int meson_ee_pwrc_on(struct generic_pm_domain *domain) if (ret) return ret; - return clk_bulk_prepare_enable(pwrc_domain->num_clks, - pwrc_domain->clks); + ret = clk_bulk_prepare_enable(pwrc_domain->num_clks, + pwrc_domain->clks); + if (ret) + return ret; + + pwrc_domain->enabled = true; + + return 0; } static int meson_ee_pwrc_init_domain(struct platform_device *pdev, @@ -434,33 +456,11 @@ static int meson_ee_pwrc_init_domain(struct platform_device *pdev, dom->base.power_on = meson_ee_pwrc_on; dom->base.power_off = meson_ee_pwrc_off; - /* - * TOFIX: This is a special case for the VPU power domain, which can - * be enabled previously by the bootloader. In this case the VPU - * pipeline may be functional but no driver maybe never attach - * to this power domain, and if the domain is disabled it could - * cause system errors. This is why the pm_domain_always_on_gov - * is used here. - * For the same reason, the clocks should be enabled in case - * we need to power the domain off, otherwise the internal clocks - * prepare/enable counters won't be in sync. - */ - if (dom->num_clks && dom->desc.get_power && !dom->desc.get_power(dom)) { - ret = clk_bulk_prepare_enable(dom->num_clks, dom->clks); - if (ret) - return ret; - - dom->base.flags = GENPD_FLAG_ALWAYS_ON; - ret = pm_genpd_init(&dom->base, NULL, false); - if (ret) - return ret; - } else { - ret = pm_genpd_init(&dom->base, NULL, - (dom->desc.get_power ? - dom->desc.get_power(dom) : true)); - if (ret) - return ret; - } + ret = pm_genpd_init(&dom->base, NULL, + (dom->desc.get_power ? + dom->desc.get_power(dom) : true)); + if (ret) + return ret; return 0; } @@ -528,19 +528,6 @@ static int meson_ee_pwrc_probe(struct platform_device *pdev) return of_genpd_add_provider_onecell(pdev->dev.of_node, &pwrc->xlate); } -static void meson_ee_pwrc_shutdown(struct platform_device *pdev) -{ - struct meson_ee_pwrc *pwrc = platform_get_drvdata(pdev); - int i; - - for (i = 0 ; i < pwrc->xlate.num_domains ; ++i) { - struct meson_ee_pwrc_domain *dom = &pwrc->domains[i]; - - if (dom->desc.get_power && !dom->desc.get_power(dom)) - meson_ee_pwrc_off(&dom->base); - } -} - static struct meson_ee_pwrc_domain_data meson_ee_g12a_pwrc_data = { .count = ARRAY_SIZE(g12a_pwrc_domains), .domains = g12a_pwrc_domains, @@ -606,7 +593,6 @@ MODULE_DEVICE_TABLE(of, meson_ee_pwrc_match_table); static struct platform_driver meson_ee_pwrc_driver = { .probe = meson_ee_pwrc_probe, - .shutdown = meson_ee_pwrc_shutdown, .driver = { .name = "meson_ee_pwrc", .of_match_table = meson_ee_pwrc_match_table, -- 2.31.1
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