From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hans de Goede Subject: Re: [PATCH v4 05/16] pwm: lpss: Use pwm_lpss_apply() when restoring state on resume Date: Thu, 9 Jul 2020 15:48:12 +0200 Message-ID: References: <20200708211432.28612-1-hdegoede@redhat.com> <20200708211432.28612-6-hdegoede@redhat.com> <20200709133609.GY3703480@smile.fi.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20200709133609.GY3703480@smile.fi.intel.com> Content-Language: en-US Sender: linux-acpi-owner@vger.kernel.org To: Andy Shevchenko Cc: Thierry Reding , =?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, Mika Westerberg , linux-acpi@vger.kernel.org List-Id: linux-pwm@vger.kernel.org Hi, On 7/9/20 3:36 PM, Andy Shevchenko wrote: > On Wed, Jul 08, 2020 at 11:14:21PM +0200, Hans de Goede wrote: >> Before this commit a suspend + resume of the LPSS PWM controller >> would result in the controller being reset to its defaults of >> output-freq = clock/256, duty-cycle=100%, until someone changes >> to the output-freq and/or duty-cycle are made. >> >> This problem has been masked so far because the main consumer >> (the i915 driver) was always making duty-cycle changes on resume. >> With the conversion of the i915 driver to the atomic PWM API the >> driver now only disables/enables the PWM on suspend/resume leaving >> the output-freq and duty as is, triggering this problem. >> >> The LPSS PWM controller has a mechanism where the ctrl register value >> and the actual base-unit and on-time-div values used are latched. When >> software sets the SW_UPDATE bit then at the end of the current PWM cycle, >> the new values from the ctrl-register will be latched into the actual >> registers, and the SW_UPDATE bit will be cleared. >> >> The problem is that before this commit our suspend/resume handling >> consisted of simply saving the PWM ctrl register on suspend and >> restoring it on resume, without setting the PWM_SW_UPDATE bit. >> When the controller has lost its state over a suspend/resume and thus >> has been reset to the defaults, just restoring the register is not >> enough. We must also set the SW_UPDATE bit to tell the controller to >> latch the restored values into the actual registers. >> >> Fixing this problem is not as simple as just or-ing in the value which >> is being restored with SW_UPDATE. If the PWM was enabled before we must >> write the new settings + PWM_SW_UPDATE before setting PWM_ENABLE. >> We must also wait for PWM_SW_UPDATE to become 0 again and depending on the >> model we must do this either before or after the setting of PWM_ENABLE. >> >> All the necessary logic for doing this is already present inside >> pwm_lpss_apply(), so instead of duplicating this inside the resume >> handler, this commit makes the resume handler use pwm_lpss_apply() to >> restore the settings when necessary. This fixes the output-freq and >> duty-cycle being reset to their defaults on resume. > > ... > >> +static int __pwm_lpss_apply(struct pwm_chip *chip, struct pwm_device *pwm, >> + const struct pwm_state *state, bool from_resume) >> { >> struct pwm_lpss_chip *lpwm = to_lpwm(chip); >> int ret; >> >> if (state->enabled) { >> if (!pwm_is_enabled(pwm)) { >> - pm_runtime_get_sync(chip->dev); >> + if (!from_resume) >> + pm_runtime_get_sync(chip->dev); >> + >> ret = pwm_lpss_is_updating(pwm); >> if (ret) { >> - pm_runtime_put(chip->dev); >> + if (!from_resume) >> + pm_runtime_put(chip->dev); >> + >> return ret; >> } >> pwm_lpss_prepare(lpwm, pwm, state->duty_cycle, state->period); >> pwm_lpss_cond_enable(pwm, lpwm->info->bypass == false); >> ret = pwm_lpss_wait_for_update(pwm); >> if (ret) { >> - pm_runtime_put(chip->dev); >> + if (!from_resume) >> + pm_runtime_put(chip->dev); >> + >> return ret; >> } >> pwm_lpss_cond_enable(pwm, lpwm->info->bypass == true); > >> } >> } else if (pwm_is_enabled(pwm)) { >> pwm_lpss_write(pwm, pwm_lpss_read(pwm) & ~PWM_ENABLE); >> - pm_runtime_put(chip->dev); >> + >> + if (!from_resume) >> + pm_runtime_put(chip->dev); >> } > > I'm wondering if splitting more will make this look better, like: > > ... > if (from_resume) { > ret = pwm_lpss_prepare_enable(...); // whatever name you think suits better > } else { > pm_runtime_get_sync(...); > ret = pwm_lpss_prepare_enable(...); > if (ret) > pm_runtime_put(...); > } > ... > That is a good idea, I like it. We already had multiple pm_runtime_put() calls before for the error handlig and this patch did not make it any better. So adding a pwm_lpss_prepare_enable() helper (the name works for) will also cleanup the original code. I will add this helper as a separate preparation patch for this one in v5 of the patch-set. Regards, Hans