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(-)
@@ -425,10 +425,17 @@ static void ltdc_crtc_atomic_enable(struct drm_crtc *crtc,{structltdc_device*ldev=crtc_to_ltdc(crtc);structdrm_device*ddev=crtc->dev;+intret;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);
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 ?
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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.
Regards,
Raphaël G-P
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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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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:
quoted hunk
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(-)
@@ -425,10 +425,17 @@ static void ltdc_crtc_atomic_enable(struct drm_crtc *crtc,{structltdc_device*ldev=crtc_to_ltdc(crtc);structdrm_device*ddev=crtc->dev;+intret;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);
{
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 ?
Hello Marek,
I've run a deeper analysis over this implementation.
If I may take rockchip's "rockchip_drm_vop.c" driver, there is an boolean "is_enabled" set to true when crtc_atomic_enable is called.
The above implementation could save us from adding such field in the ltdc_dev structure.
Another solution could be in order to simply call pm_runtime_get_sync() in ltdc_crtc_mode_set_nofb() and by removing this condition in ltdc_atomic_crtc_disable() the driver behaves just like the first version of this patch.
In this way, it avoids such conditions and seems more to get along with the current implementation.
Regards,
Raphaël
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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 ?
Hello Marek,
Hi,
I've run a deeper analysis over this implementation.
Thank you
If I may take rockchip's "rockchip_drm_vop.c" driver, there is an boolean "is_enabled" set to true when crtc_atomic_enable is called.
The above implementation could save us from adding such field in the ltdc_dev structure.
Another solution could be in order to simply call pm_runtime_get_sync() in ltdc_crtc_mode_set_nofb() and by removing this condition in ltdc_atomic_crtc_disable() the driver behaves just like the first version of this patch.
In this way, it avoids such conditions and seems more to get along with the current implementation.
Let me maybe ask a different question -- can ltdc_crtc_mode_set_nofb()
ever be called with the LTDC suspended (so you would have to call
pm_runtime_get_sync() in that function to power the block up and to get
access to its registers) ?
[...]
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