From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b="KBC8zUjQ" Received: from madras.collabora.co.uk (madras.collabora.co.uk [46.235.227.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5277A1BDF; Wed, 29 Nov 2023 05:28:40 -0800 (PST) Received: from [100.94.55.57] (cola.collaboradmins.com [195.201.22.229]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: ehristev) by madras.collabora.co.uk (Postfix) with ESMTPSA id 4D8346607323; Wed, 29 Nov 2023 13:28:38 +0000 (GMT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1701264519; bh=voQon3LzdEu0qMz+wUEU2I4h6CzbZywQZscFJYWwvfA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=KBC8zUjQWLT/3o9MkGNsKM9HzFusQO2gclXA4e+ncAKdAwzQD7ggdJ2s45jz5d1zw f/dopADVQm2q5CqKN7wQX7iRo8FNW4usmTXD6mKP/vFx8/dwE8Wgr0athzafXzu++s ZBGj11YJiU+mSeGwJAGJIee67h8WlsOxcxgcZeebSY1Tq7kKNId+yKIMo55QIOvjBd dJISR+s4MPA6UoaVbu/zLPQ8rfjocnt6yJ2drSCGUYOVCfG0HxSLhRnEbx84Pwiy2Y wW7baJMLTI88PsVv4XKPfQ7wMqRMimDG3AEqPMkhNT6ifLkOovmA39Z2a3m5bmVgZD qW0KTmySgU16w== Message-ID: Date: Wed, 29 Nov 2023 15:28:35 +0200 Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] pmdomain: mediatek: fix race condition in power on/power off sequences Content-Language: en-US To: AngeloGioacchino Del Regno , linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, linux-pm@vger.kernel.org Cc: eballetbo@kernel.org, ulf.hansson@linaro.org, linux-kernel@vger.kernel.org, kernel@collabora.com References: <20231129113120.4907-1-eugen.hristev@collabora.com> From: Eugen Hristev In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 11/29/23 14:52, AngeloGioacchino Del Regno wrote: > 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 > > 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. What I see in my tests, is that a power on call for SSUSB domain happens while the previous power off sequence did not yet complete, most likely while it's waiting in readx_poll_timeout . This leads to inconsistency of the power domain, not getting the ACKs next time a power on attempt occurs. I understand what you say about locks, but in this case the powering off is not called by the genpd itself, but rather it's called by the rollback probe failed mechanism : when the probing fails, scpsys_domain_cleanup() is called during the same probing session. Then it happens that probing begins again and previous cleanup is not yet completed. I am not sure whether the lock is still held from the previous run, but it's clearly not waiting for a lock to be released to be called again. > > 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 >>   #include >>   #include >> +#include >>   #include >>   #include >>   #include >> @@ -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; > >