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[2001:1c00:c0c:fe00:d2ea:f29d:118b:24dc]) by smtp.gmail.com with ESMTPSA id r16sm2909233ejb.110.2020.09.03.04.12.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 03 Sep 2020 04:12:32 -0700 (PDT) Subject: Re: [PATCH v9 06/17] pwm: lpss: Make pwm_lpss_apply() not rely on existing hardware state To: Thierry Reding Cc: =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= , "Rafael J . Wysocki" , Len Brown , linux-pwm@vger.kernel.org, intel-gfx , dri-devel@lists.freedesktop.org, Andy Shevchenko , Mika Westerberg , linux-acpi@vger.kernel.org References: <20200903105114.9969-1-hdegoede@redhat.com> <20200903105114.9969-7-hdegoede@redhat.com> <20200903105909.GA3756465@ulmo> From: Hans de Goede Message-ID: Date: Thu, 3 Sep 2020 13:12:31 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200903105909.GA3756465@ulmo> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-pwm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pwm@vger.kernel.org Hi, On 9/3/20 12:59 PM, Thierry Reding wrote: > On Thu, Sep 03, 2020 at 12:51:03PM +0200, Hans de Goede wrote: >> Before this commit pwm_lpss_apply() was making 2 assuming >> 2 pre-conditions were met by the existing hardware state: > > I think that "making 2" is too much. You're right at first the sentence had something about making 2 assumptions, then I added pre-conditions in there for it to better describe the problem... >> 1. That the base-unit and on-time-div read back from the >> control register are those actually in use, so that it >> can skip setting the update bit if the read-back value >> matches the desired values. >> >> 2. That the controller is enabled when the cached >> pwm_state.enabled says that the controller is enabled. >> >> As the long history of fixes for subtle (often suspend/resume) >> lpss-pwm issues shows, this assumptions are not necessary >> always true. >> >> 1. Specifically is not true on some (*) Cherry Trail devices >> with a nasty GFX0._PS3 method which: a. saves the ctrl reg value. >> b. sets the base-unit to 0 and writes the update bit to apply/commit >> c. restores the original ctrl value without setting the update bit, >> so that the 0 base-unit value is still in use. >> >> 2. Assumption 2. currently is true, but only because of the code which >> saves/restores the state on suspend/resume. By convention restoring the >> PWM state should be done by the PWM consumer and the presence of this >> code in the pmw-lpss driver is a bug. Therefor the save/restore code will >> be dropped in the next patch in this series, after which this assumption >> also is no longer true. >> >> This commit changes the pwm_lpss_apply() to make any assumptions about the > > Did you mean to say "... to _not_ make any assumptions ..."? Yes, oops. That is a small but important difference. I'll do a v10 with your 2 Acked-by's added and both commit msg issues fixed. Hopefully that will be the last version. >> state the hardware is in. Instead it makes pwm_lpss_apply() always fully >> program the PWM controller, making it much less fragile. >> >> *) Seen on the Acer One 10 S1003, Lenovo Ideapad Miix 310 and 320 models >> and various Medion models. >> >> Signed-off-by: Hans de Goede >> --- >> drivers/pwm/pwm-lpss.c | 21 +++++++++------------ >> 1 file changed, 9 insertions(+), 12 deletions(-) > > Other than the two small nits, this looks much more idiomatic and true > to the atomic API, so: > > Acked-by: Thierry Reding Thank you. Regards, Hans