Messages in this thread Patch in this message | | | Date | Wed, 29 Nov 2023 13:52:40 +0100 | Subject | Re: [PATCH] pmdomain: mediatek: fix race condition in power on/power off sequences | From | AngeloGioacchino Del Regno <> |
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Il 29/11/23 12:31, Eugen Hristev ha scritto: > It can happen that during the power off sequence for a power domain > another power on sequence is started, and it can lead to powering on and > off in the same time for the similar power domain. > This can happen if parallel probing occurs: one device starts probing, and > one power domain is probe deferred, this leads to all power domains being > rolled back and powered off, while in the same time another device starts > probing and requests powering on the same power domains or similar. > > This was encountered on MT8186, when the sequence is : > Power on SSUSB > Power on SSUSB_P1 > Power on DIS > -> probe deferred > Power off DIS > Power off SSUSB_P1 > Power off SSUSB > > During the sequence of powering off SSUSB, some new similar sequence starts, > and during the power on of SSUSB, clocks are enabled. > In this case, powering off SSUSB fails from the first sequence, because > power off ACK bit check times out (as clocks are powered back on by the second > sequence). In consequence, powering it on also times out, and it leads to > the whole power domain in a bad state. > > To solve this issue, added a mutex that locks the whole power off/power on > sequence such that it would never happen that multiple sequences try to > enable or disable the same power domain in parallel. > > Fixes: 59b644b01cf4 ("soc: mediatek: Add MediaTek SCPSYS power domains") > Signed-off-by: Eugen Hristev <eugen.hristev@collabora.com>
I don't think that it's a race between genpd_power_on() and genpd_power_off() calls at all, because genpd *does* have locking after all... at least for probe and for parents of a power domain (and more anyway).
As far as I remember, what happens when you start .probe()'ing a device is: platform_probe() -> dev_pm_domain_attach() -> genpd_dev_pm_attach()
There, you end up with
if (power_on) { genpd_lock(pd); ret = genpd_power_on(pd, 0); genpd_unlock(pd); }
...but when you fail probing, you go with genpd_dev_pm_detach(), which then calls
/* Check if PM domain can be powered off after removing this device. */ genpd_queue_power_off_work(pd);
but even then, you end up being in a worker doing
genpd_lock(genpd); genpd_power_off(genpd, false, 0); genpd_unlock(genpd);
...so I don't understand why this mutex can resolve the situation here (also: are you really sure that the race is solved like that?)
I'd say that this probably needs more justification and a trace of the actual situation here.
Besides, if this really resolves the issue, I would prefer seeing variants of scpsys_power_{on,off}() functions, because we anyway don't need to lock mutexes during this driver's probe (add_subdomain calls scpsys_power_on()). In that case, `scpsys_power_on_unlocked()` would be an idea... but still, please analyze why your solution works, if it does, because I'm not convinced.
Cheers, Angelo
> --- > drivers/pmdomain/mediatek/mtk-pm-domains.c | 24 +++++++++++++++++----- > 1 file changed, 19 insertions(+), 5 deletions(-) > > diff --git a/drivers/pmdomain/mediatek/mtk-pm-domains.c b/drivers/pmdomain/mediatek/mtk-pm-domains.c > index d5f0ee05c794..4f136b47e539 100644 > --- a/drivers/pmdomain/mediatek/mtk-pm-domains.c > +++ b/drivers/pmdomain/mediatek/mtk-pm-domains.c > @@ -9,6 +9,7 @@ > #include <linux/io.h> > #include <linux/iopoll.h> > #include <linux/mfd/syscon.h> > +#include <linux/mutex.h> > #include <linux/of.h> > #include <linux/of_clk.h> > #include <linux/platform_device.h> > @@ -56,6 +57,7 @@ struct scpsys { > struct device *dev; > struct regmap *base; > const struct scpsys_soc_data *soc_data; > + struct mutex mutex; > struct genpd_onecell_data pd_data; > struct generic_pm_domain *domains[]; > }; > @@ -238,9 +240,13 @@ static int scpsys_power_on(struct generic_pm_domain *genpd) > bool tmp; > int ret; > > + mutex_lock(&scpsys->mutex); > + > ret = scpsys_regulator_enable(pd->supply); > - if (ret) > + if (ret) { > + mutex_unlock(&scpsys->mutex); > return ret; > + } > > ret = clk_bulk_prepare_enable(pd->num_clks, pd->clks); > if (ret) > @@ -291,6 +297,7 @@ static int scpsys_power_on(struct generic_pm_domain *genpd) > goto err_enable_bus_protect; > } > > + mutex_unlock(&scpsys->mutex); > return 0; > > err_enable_bus_protect: > @@ -305,6 +312,7 @@ static int scpsys_power_on(struct generic_pm_domain *genpd) > clk_bulk_disable_unprepare(pd->num_clks, pd->clks); > err_reg: > scpsys_regulator_disable(pd->supply); > + mutex_unlock(&scpsys->mutex); > return ret; > } > > @@ -315,13 +323,15 @@ static int scpsys_power_off(struct generic_pm_domain *genpd) > bool tmp; > int ret; > > + mutex_lock(&scpsys->mutex); > + > ret = scpsys_bus_protect_enable(pd); > if (ret < 0) > - return ret; > + goto err_mutex_unlock; > > ret = scpsys_sram_disable(pd); > if (ret < 0) > - return ret; > + goto err_mutex_unlock; > > if (pd->data->ext_buck_iso_offs && MTK_SCPD_CAPS(pd, MTK_SCPD_EXT_BUCK_ISO)) > regmap_set_bits(scpsys->base, pd->data->ext_buck_iso_offs, > @@ -340,13 +350,15 @@ static int scpsys_power_off(struct generic_pm_domain *genpd) > ret = readx_poll_timeout(scpsys_domain_is_on, pd, tmp, !tmp, MTK_POLL_DELAY_US, > MTK_POLL_TIMEOUT); > if (ret < 0) > - return ret; > + goto err_mutex_unlock; > > clk_bulk_disable_unprepare(pd->num_clks, pd->clks); > > scpsys_regulator_disable(pd->supply); > > - return 0; > +err_mutex_unlock: > + mutex_unlock(&scpsys->mutex); > + return ret; > } > > static struct > @@ -700,6 +712,8 @@ static int scpsys_probe(struct platform_device *pdev) > return PTR_ERR(scpsys->base); > } > > + mutex_init(&scpsys->mutex); > + > ret = -ENODEV; > for_each_available_child_of_node(np, node) { > struct generic_pm_domain *domain;
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