Re: [PATCH] drm/stm: ltdc: improve pm_runtime to stop clocks

[yannick Fertre]

Hi Raphaël,

thanks for the patch.

Tested-by: Yannick Fertre <yannick.fertre@xxxxxxxxxxx>



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@xxxxxxxxxxx>
> ---
>   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);
>