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<p class="MsoNormal"><span lang="EN-US">On Fri, Jan 20, 2023 at 01:00:18PM +0100, Uwe Kleine-König wrote:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> Most but not all PWMs drive the PWM pin to its inactive state when<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> disabled. However if there is no enable_gpio and no regulator the PWM<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> must drive the inactive state to actually disable the backlight.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> So keep the PWM on in this case.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> Note that to determine if there is a regulator some effort is required<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> because it might happen that there isn't actually one but the regulator<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> core gave us a dummy. (A nice side effect is that this makes the<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> regulator actually optional even on fully constrained systems.)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> This fixes backlight disabling e.g. on i.MX6 when an inverted PWM is<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> used.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> Hint for the future: If this change results in a regression, the bug is<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> in the lowlevel PWM driver.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> Signed-off-by: Uwe Kleine-König <a href="mailto:u.kleine-koenig@pengutronix.de">
u.kleine-koenig@pengutronix.de</a><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">This patch broke imx7ulp suspend resume and got the following error:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Freezing remaining freezable tasks<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Freezing remaining freezable tasks completed (elapsed 0.001 seconds)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">printk: Suspending console(s) (use no_console_suspend to debug)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">asix 1-1:1.0 eth0: Link is Down<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">imx7ulp-tpm-pwm 40250000.pwm: PM: dpm_run_callback(): platform_pm_suspend+0x0/0x48 returns -16<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">imx7ulp-tpm-pwm 40250000.pwm: PM: failed to suspend: error -16<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">…<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">It seems this patch changed the behavior of pwm_backlight_suspend a little bit in<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">pwm_backlight_power_off() that pwm state keep unchanged during suspend.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Then pwm_imx_tpm_suspend() will return -Ebusy due to tpm->enable_count > 0.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Was this intended behavior? Should we fix pwm core or the driver?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Regards<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Aisheng<o:p></o:p></span></p>
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