Messages in this thread | | | Subject | Re: [PATCH] drm/stm: ltdc: improve pm_runtime to stop clocks | From | Marek Vasut <> | Date | Fri, 2 Jul 2021 20:07:34 +0200 |
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On 7/2/21 11:23 AM, Raphael Gallais-Pou wrote: > Hello Marek,
Hi,
> Sorry for the late answer.
No worries, take your time
> On 6/30/21 2:35 AM, Marek Vasut wrote: >> On 6/29/21 1:58 PM, Raphael GALLAIS-POU - foss wrote: >> >> [...] >> >>> +++ b/drivers/gpu/drm/stm/ltdc.c >>> @@ -425,10 +425,17 @@ static void ltdc_crtc_atomic_enable(struct >>> drm_crtc *crtc, >>> { >>> struct ltdc_device *ldev = crtc_to_ltdc(crtc); >>> struct drm_device *ddev = crtc->dev; >>> + int ret; >>> DRM_DEBUG_DRIVER("\n"); >>> - pm_runtime_get_sync(ddev->dev); >>> + if (!pm_runtime_active(ddev->dev)) { >>> + ret = pm_runtime_get_sync(ddev->dev); >> >> All these if (!pm_runtime_active()) then pm_runtime_get_sync() calls >> look like workaround for some larger issue. Shouldn't the pm_runtime >> do some refcounting on its own , so this shouldn't be needed ? > > > This problem purely comes from the driver internals, so I don't think it > is a workaround. > > Because of the "ltdc_crtc_mode_set_nofb" function which does not have > any "symmetrical" call, such as enable/disable functions, there was two > calls to pm_runtime_get_sync against one call to pm_runtime_put_sync. > > This instability resulted in the LTDC clocks being always enabled, even > when the peripheral was disabled. This could be seen in the clk_summary > as explained in the patch summary among other things. > > By doing so, we first check if the clocks are not already activated, and > in that case we call pm_runtime_get_sync.
I just have to wonder, how come other drivers don't need these if (!pm_runtime_active()) pm_runtime_get_sync() conditions. I think they just get/put the runtime PM within a call itself, not across function calls. Maybe that could be the right fix here too ?
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