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SubjectRe: [PATCH] drm/stm: ltdc: improve pm_runtime to stop clocks
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Hi Raphaël,

thanks for the patch.

Tested-by: Yannick Fertre <yannick.fertre@foss.st.com>



On 6/29/21 1:58 PM, Raphael GALLAIS-POU - foss wrote:
> Bugzilla ticket: https://intbugzilla.st.com/show_bug.cgi?id=60620
> Gerrit patch: https://gerrit.st.com/c/mpu/oe/st/linux-stm32/+/208093/
>
> In the LTDC driver, pm_runtime_get_sync was wrongly used and caused the
> LTDC pixel clock to be systematically enabled in the clock summary.
>
> After one simple use of the LTDC by activating and deactivating,
> the clock summary results as below:
>
> ~# cat /sys/kernel/debug/clk/clk_summary | grep ltdc
> ltdc_px 1 1 0 29700000 0 0 50000 N
> ltdc 0 0 0 133250000 0 0 50000 N
>
> By doing so, pm_runtime_get_sync only increments the clock counter when
> the driver was in not active, displaying the right information when the
> LTDC is not in use, resulting of the below clock summary after deactivation
> of the LTDC.
>
> ~# cat /sys/kernel/debug/clk/clk_summary | grep ltdc
> ltdc_px 0 0 0 29700000 0 0 50000 N
> ltdc 0 0 0 133250000 0 0 50000 N
>
> The clocks are activated either by the crtc_set_nofb function or
> by the crtc_atomic_enable function. A check of pm_runtime activity must
> be done before set clocks on. This check must also be done for others
> functions which access registers.
>
> Signed-off-by: Raphael Gallais-Pou <raphael.gallais-pou@foss.st.com>
> ---
> drivers/gpu/drm/stm/ltdc.c | 21 ++++++++++++++++++++-
> 1 file changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
> index 08b71248044d..bf9d18023698 100644
> --- a/drivers/gpu/drm/stm/ltdc.c
> +++ 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);
> + if (ret) {
> + DRM_ERROR("Failed to set mode, cannot get sync\n");
> + return;
> + }
> + }
>
> /* Sets the background color value */
> reg_write(ldev->regs, LTDC_BCCR, BCCR_BCBLACK);
> @@ -783,6 +790,7 @@ static void ltdc_plane_atomic_update(struct drm_plane *plane,
> struct drm_plane_state *newstate = drm_atomic_get_new_plane_state(state,
> plane);
> struct drm_framebuffer *fb = newstate->fb;
> + struct drm_device *ddev = plane->dev;
> u32 lofs = plane->index * LAY_OFS;
> u32 x0 = newstate->crtc_x;
> u32 x1 = newstate->crtc_x + newstate->crtc_w - 1;
> @@ -792,6 +800,11 @@ static void ltdc_plane_atomic_update(struct drm_plane *plane,
> u32 val, pitch_in_bytes, line_length, paddr, ahbp, avbp, bpcr;
> enum ltdc_pix_fmt pf;
>
> + if (!pm_runtime_active(ddev->dev)) {
> + DRM_DEBUG_DRIVER("crtc not activated");
> + return;
> + }
> +
> if (!newstate->crtc || !fb) {
> DRM_DEBUG_DRIVER("fb or crtc NULL");
> return;
> @@ -897,8 +910,14 @@ static void ltdc_plane_atomic_disable(struct drm_plane *plane,
> struct drm_plane_state *oldstate = drm_atomic_get_old_plane_state(state,
> plane);
> struct ltdc_device *ldev = plane_to_ltdc(plane);
> + struct drm_device *ddev = plane->dev;
> u32 lofs = plane->index * LAY_OFS;
>
> + if (!pm_runtime_active(ddev->dev)) {
> + DRM_DEBUG_DRIVER("crtc already deactivated");
> + return;
> + }
> +
> /* disable layer */
> reg_clear(ldev->regs, LTDC_L1CR + lofs, LXCR_LEN);
>
>

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