[PATCH 1/2] drm/rockchip: vop: clear DMA stop bit on flush on RK3066

[PATCH 1/2] drm/rockchip: vop: clear DMA stop bit on flush on RK3066

[Val Packett]

On the RK3066, there is a bit that must be cleared on flush, otherwise
we do not get display output (at least for RGB).

Signed-off-by: Val Packett <val@packett.cool>
Cc: stable@vger.kernel.org
---
Hi! This was required to get display working on an old RK3066 tablet,
along with the next tiny patch in the series enabling the RGB output.

I have spent quite a lot of time banging my head against the wall debugging
that display (especially since at the same time a scaler chip is used for
LVDS encoding), but finally adding debug prints showed that RK3066_SYS_CTRL0
ended up being reset to all-zero after being written correctly upon init.
Looking at the register definitions in the vendor driver revealed that the
reason was pretty self-explanatory: "dma_stop".
---
 drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 3 +++
 drivers/gpu/drm/rockchip/rockchip_drm_vop.h | 1 +
 drivers/gpu/drm/rockchip/rockchip_vop_reg.c | 1 +
 3 files changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
index a13473b2d..d4daeba74 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
@@ -1578,6 +1578,9 @@ static void vop_crtc_atomic_flush(struct drm_crtc *crtc,
 
 	spin_lock(&vop->reg_lock);
 
+	/* If the chip has a DMA stop bit (RK3066), it must be cleared. */
+	VOP_REG_SET(vop, common, dma_stop, 0);
+
 	/* Enable AFBC if there is some AFBC window, disable otherwise. */
 	s = to_rockchip_crtc_state(crtc->state);
 	VOP_AFBC_SET(vop, enable, s->enable_afbc);
diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.h b/drivers/gpu/drm/rockchip/rockchip_drm_vop.h
index b33e5bdc2..0cf512cc1 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.h
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.h
@@ -122,6 +122,7 @@ struct vop_common {
 	struct vop_reg lut_buffer_index;
 	struct vop_reg gate_en;
 	struct vop_reg mmu_en;
+	struct vop_reg dma_stop;
 	struct vop_reg out_mode;
 	struct vop_reg standby;
 };
diff --git a/drivers/gpu/drm/rockchip/rockchip_vop_reg.c b/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
index b9ee02061..9bcb40a64 100644
--- a/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
+++ b/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
@@ -466,6 +466,7 @@ static const struct vop_output rk3066_output = {
 };
 
 static const struct vop_common rk3066_common = {
+	.dma_stop = VOP_REG(RK3066_SYS_CTRL0, 0x1, 0),
 	.standby = VOP_REG(RK3066_SYS_CTRL0, 0x1, 1),
 	.out_mode = VOP_REG(RK3066_DSP_CTRL0, 0xf, 0),
 	.cfg_done = VOP_REG(RK3066_REG_CFG_DONE, 0x1, 0),
-- 
2.45.0

[PATCH 2/2] drm/rockchip: vop: enable VOP_FEATURE_INTERNAL_RGB on RK3066

[Val Packett]

Signed-off-by: Val Packett <val@packett.cool>
Cc: stable@vger.kernel.org
---
 drivers/gpu/drm/rockchip/rockchip_vop_reg.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/rockchip/rockchip_vop_reg.c b/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
index 9bcb40a64..e2c6ba26f 100644
--- a/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
+++ b/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
@@ -515,6 +515,7 @@ static const struct vop_data rk3066_vop = {
 	.output = &rk3066_output,
 	.win = rk3066_vop_win_data,
 	.win_size = ARRAY_SIZE(rk3066_vop_win_data),
+	.feature = VOP_FEATURE_INTERNAL_RGB,
 	.max_output = { 1920, 1080 },
 };
 
-- 
2.45.0

Re: [PATCH 2/2] drm/rockchip: vop: enable VOP_FEATURE_INTERNAL_RGB on RK3066

[Greg KH]

On Sun, May 19, 2024 at 04:31:32AM -0300, Val Packett wrote:
> Signed-off-by: Val Packett <val@packett.cool>
> Cc: stable@vger.kernel.org
> ---
>  drivers/gpu/drm/rockchip/rockchip_vop_reg.c | 1 +
>  1 file changed, 1 insertion(+)

Maybe the DRM subsystem has more lax rules, but I know I can't take
patches without any changelog text at all, sorry.

greg k-h

Re: [PATCH 1/2] drm/rockchip: vop: clear DMA stop bit on flush on RK3066

[Greg KH]

On Sun, May 19, 2024 at 04:31:31AM -0300, Val Packett wrote:
> On the RK3066, there is a bit that must be cleared on flush, otherwise
> we do not get display output (at least for RGB).
> 
> Signed-off-by: Val Packett <val@packett.cool>
> Cc: stable@vger.kernel.org
> ---
> Hi! This was required to get display working on an old RK3066 tablet,
> along with the next tiny patch in the series enabling the RGB output.
> 
> I have spent quite a lot of time banging my head against the wall debugging
> that display (especially since at the same time a scaler chip is used for
> LVDS encoding), but finally adding debug prints showed that RK3066_SYS_CTRL0
> ended up being reset to all-zero after being written correctly upon init.
> Looking at the register definitions in the vendor driver revealed that the
> reason was pretty self-explanatory: "dma_stop".

What commit id does this fix?

thanks,

greg k-h

Re: [PATCH 1/2] drm/rockchip: vop: clear DMA stop bit on flush on RK3066

[Val Packett]

On Sun, May 19 2024 at 09:59:47 +02:00:00, Greg KH 
<gregkh@linuxfoundation.org> wrote:
> On Sun, May 19, 2024 at 04:31:31AM -0300, Val Packett wrote:
>>  On the RK3066, there is a bit that must be cleared on flush, 
>> otherwise
>>  we do not get display output (at least for RGB).
> 
> What commit id does this fix?

I guess: f4a6de855e "drm: rockchip: vop: add rk3066 vop definitions" ?

But similar changes like:
742203cd "drm: rockchip: add missing registers for RK3066"
8d544233 "drm/rockchip: vop: Add directly output rgb feature for px30"
did not have any "Fixes" reference.

~val

Re: [PATCH 1/2] drm/rockchip: vop: clear DMA stop bit on flush on RK3066

[Greg KH]

On Sun, May 19, 2024 at 05:38:24AM -0300, Val Packett wrote:
> 
> 
> On Sun, May 19 2024 at 09:59:47 +02:00:00, Greg KH
> <gregkh@linuxfoundation.org> wrote:
> > On Sun, May 19, 2024 at 04:31:31AM -0300, Val Packett wrote:
> > >  On the RK3066, there is a bit that must be cleared on flush,
> > > otherwise
> > >  we do not get display output (at least for RGB).
> > 
> > What commit id does this fix?
> 
> I guess: f4a6de855e "drm: rockchip: vop: add rk3066 vop definitions" ?

Great, can you add a Fixes: tag when you resend these?

> But similar changes like:
> 742203cd "drm: rockchip: add missing registers for RK3066"
> 8d544233 "drm/rockchip: vop: Add directly output rgb feature for px30"
> did not have any "Fixes" reference.

Just because people didn't properly tag things in the past, doesn't mean
you should perpetuate that problem :)

thanks,

greg k-h

[PATCH v2 1/2] drm/rockchip: vop: clear DMA stop bit upon vblank on RK3066

[Val Packett]

On the RK3066, there is a bit that must be cleared, otherwise
the picture does not show up on the display (at least for RGB).

Fixes: f4a6de8 ("drm: rockchip: vop: add rk3066 vop definitions")
Cc: stable@vger.kernel.org
Signed-off-by: Val Packett <val@packett.cool>
---
v2: doing this on vblank makes more sense; added fixes tag
---
 drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 6 ++++++
 drivers/gpu/drm/rockchip/rockchip_drm_vop.h | 1 +
 drivers/gpu/drm/rockchip/rockchip_vop_reg.c | 1 +
 3 files changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
index a13473b2d..2731fe2b2 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
@@ -1766,6 +1766,12 @@ static void vop_handle_vblank(struct vop *vop)
 	}
 	spin_unlock(&drm->event_lock);
 
+	if (VOP_HAS_REG(vop, common, dma_stop)) {
+		spin_lock(&vop->reg_lock);
+		VOP_REG_SET(vop, common, dma_stop, 0);
+		spin_unlock(&vop->reg_lock);
+	}
+
 	if (test_and_clear_bit(VOP_PENDING_FB_UNREF, &vop->pending))
 		drm_flip_work_commit(&vop->fb_unref_work, system_unbound_wq);
 }
diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.h b/drivers/gpu/drm/rockchip/rockchip_drm_vop.h
index b33e5bdc2..0cf512cc1 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.h
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.h
@@ -122,6 +122,7 @@ struct vop_common {
 	struct vop_reg lut_buffer_index;
 	struct vop_reg gate_en;
 	struct vop_reg mmu_en;
+	struct vop_reg dma_stop;
 	struct vop_reg out_mode;
 	struct vop_reg standby;
 };
diff --git a/drivers/gpu/drm/rockchip/rockchip_vop_reg.c b/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
index b9ee02061..9bcb40a64 100644
--- a/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
+++ b/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
@@ -466,6 +466,7 @@ static const struct vop_output rk3066_output = {
 };
 
 static const struct vop_common rk3066_common = {
+	.dma_stop = VOP_REG(RK3066_SYS_CTRL0, 0x1, 0),
 	.standby = VOP_REG(RK3066_SYS_CTRL0, 0x1, 1),
 	.out_mode = VOP_REG(RK3066_DSP_CTRL0, 0xf, 0),
 	.cfg_done = VOP_REG(RK3066_REG_CFG_DONE, 0x1, 0),
-- 
2.45.1

[PATCH v2 2/2] drm/rockchip: vop: enable VOP_FEATURE_INTERNAL_RGB on RK3066

[Val Packett]

The RK3066 does have RGB display output, so it should be marked as such.

Fixes: f4a6de8 ("drm: rockchip: vop: add rk3066 vop definitions")
Cc: stable@vger.kernel.org
Signed-off-by: Val Packett <val@packett.cool>
---
v2: expanded commit message
---
 drivers/gpu/drm/rockchip/rockchip_vop_reg.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/rockchip/rockchip_vop_reg.c b/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
index 9bcb40a64..e2c6ba26f 100644
--- a/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
+++ b/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
@@ -515,6 +515,7 @@ static const struct vop_data rk3066_vop = {
 	.output = &rk3066_output,
 	.win = rk3066_vop_win_data,
 	.win_size = ARRAY_SIZE(rk3066_vop_win_data),
+	.feature = VOP_FEATURE_INTERNAL_RGB,
 	.max_output = { 1920, 1080 },
 };
 
-- 
2.45.1

Re: [PATCH v2 1/2] drm/rockchip: vop: clear DMA stop bit upon vblank on RK3066

[Heiko Stübner]

Hi Val,

Am Montag, 27. Mai 2024, 09:16:33 CEST schrieb Val Packett:
> On the RK3066, there is a bit that must be cleared, otherwise
> the picture does not show up on the display (at least for RGB).
> 
> Fixes: f4a6de8 ("drm: rockchip: vop: add rk3066 vop definitions")
> Cc: stable@vger.kernel.org
> Signed-off-by: Val Packett <val@packett.cool>
> ---
> v2: doing this on vblank makes more sense; added fixes tag

can you give a rationale for this please?

I.e. does this dma-stop bit need to be set on each vblank that happens
to push this frame to the display somehow?

Because at least in theory atomic_flush where this was living in in v1,
might happen at a slower interval?


Thanks
Heiko

> ---
>  drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 6 ++++++
>  drivers/gpu/drm/rockchip/rockchip_drm_vop.h | 1 +
>  drivers/gpu/drm/rockchip/rockchip_vop_reg.c | 1 +
>  3 files changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> index a13473b2d..2731fe2b2 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> @@ -1766,6 +1766,12 @@ static void vop_handle_vblank(struct vop *vop)
>  	}
>  	spin_unlock(&drm->event_lock);
>  
> +	if (VOP_HAS_REG(vop, common, dma_stop)) {
> +		spin_lock(&vop->reg_lock);
> +		VOP_REG_SET(vop, common, dma_stop, 0);
> +		spin_unlock(&vop->reg_lock);
> +	}
> +
>  	if (test_and_clear_bit(VOP_PENDING_FB_UNREF, &vop->pending))
>  		drm_flip_work_commit(&vop->fb_unref_work, system_unbound_wq);
>  }
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.h b/drivers/gpu/drm/rockchip/rockchip_drm_vop.h
> index b33e5bdc2..0cf512cc1 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.h
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.h
> @@ -122,6 +122,7 @@ struct vop_common {
>  	struct vop_reg lut_buffer_index;
>  	struct vop_reg gate_en;
>  	struct vop_reg mmu_en;
> +	struct vop_reg dma_stop;
>  	struct vop_reg out_mode;
>  	struct vop_reg standby;
>  };
> diff --git a/drivers/gpu/drm/rockchip/rockchip_vop_reg.c b/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
> index b9ee02061..9bcb40a64 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
> +++ b/drivers/gpu/drm/rockchip/rockchip_vop_reg.c
> @@ -466,6 +466,7 @@ static const struct vop_output rk3066_output = {
>  };
>  
>  static const struct vop_common rk3066_common = {
> +	.dma_stop = VOP_REG(RK3066_SYS_CTRL0, 0x1, 0),
>  	.standby = VOP_REG(RK3066_SYS_CTRL0, 0x1, 1),
>  	.out_mode = VOP_REG(RK3066_DSP_CTRL0, 0xf, 0),
>  	.cfg_done = VOP_REG(RK3066_REG_CFG_DONE, 0x1, 0),
> 

Re: [PATCH v2 1/2] drm/rockchip: vop: clear DMA stop bit upon vblank on RK3066

[Val Packett]

On Mon, May 27 2024 at 22:43:18 +02:00:00, Heiko Stübner 
<heiko@sntech.de> wrote:
> Hi Val,
> 
> Am Montag, 27. Mai 2024, 09:16:33 CEST schrieb Val Packett:
>>  On the RK3066, there is a bit that must be cleared, otherwise
>>  the picture does not show up
>> on the display (at least for RGB).
>> 
>>  Fixes: f4a6de8 ("drm: rockchip: vop: add rk3066 vop definitions")
>>  Cc: stable@vger.kernel.org
>>  Signed-off-by: Val Packett <val@packett.cool>
>>  ---
>>  v2: doing this on vblank makes more sense; added fixes tag
> 
> can you give a rationale for this please?
> 
> I.e. does this dma-stop bit need to be set on each vblank that happens
> to push this frame to the display somehow?


The only things I'm 100% sure about:

- that bit is called dma_stop in the Android kernel's header;
- without ever setting that bit to 1, it was getting set to 1 by the 
chip itself, as logging the register on flush was showing a 1 in that 
position (it was the only set bit - I guess others aren't readable 
after cfg_done?);
- without clearing it "between" frames, the whole screen is always 
filled with noise, the picture is not visible.

The rest is at least a bit (ha) speculative:

As I understand from what the name implies, the hardware sets it to 
indicate that it has scanned out the frame and is waiting for 
acknowledgment (clearing) to be able to scan out the next frame. I 
guess it's a redundant synchronization mechanism that was removed in 
later iterations of the VOP hardware block.

I've been trying to see if moving where I clear the bit affects the 
sort-of-tearing-but-vertical glitches that sometimes happen, especially 
early on after the system has just booted, but that seems to be 
completely unrelated pixel clock craziness (the Android kernel runs the 
screen at 66 fps, interestingly).

I'm fairly confident that both places are "correct". The reason I'm 
more on the side of vblank now is that it made logical sense to me when 
I thought about it more: acknowledging that the frame has been scanned 
out is a reaction to the frame having been scanned out. It's a 
consequence of *that* that the acknowledgment is required for the next 
frame to be drawn.

Unless we can get the opinion of someone closely familiar with this 
decade-old hardware, we only have this reasoning to go off of :)

~val
> 

Re: [PATCH v2 1/2] drm/rockchip: vop: clear DMA stop bit upon vblank on RK3066

[Heiko Stübner]

Hey,

Am Dienstag, 28. Mai 2024, 00:13:59 CEST schrieb Val Packett:
> On Mon, May 27 2024 at 22:43:18 +02:00:00, Heiko Stübner 
> <heiko@sntech.de> wrote:
> > Am Montag, 27. Mai 2024, 09:16:33 CEST schrieb Val Packett:
> >>  On the RK3066, there is a bit that must be cleared, otherwise
> >>  the picture does not show up
> >> on the display (at least for RGB).
> >> 
> >>  Fixes: f4a6de8 ("drm: rockchip: vop: add rk3066 vop definitions")
> >>  Cc: stable@vger.kernel.org
> >>  Signed-off-by: Val Packett <val@packett.cool>
> >>  ---
> >>  v2: doing this on vblank makes more sense; added fixes tag
> > 
> > can you give a rationale for this please?
> > 
> > I.e. does this dma-stop bit need to be set on each vblank that happens
> > to push this frame to the display somehow?
> 
> 
> The only things I'm 100% sure about:
> 
> - that bit is called dma_stop in the Android kernel's header;
> - without ever setting that bit to 1, it was getting set to 1 by the 
> chip itself, as logging the register on flush was showing a 1 in that 
> position (it was the only set bit - I guess others aren't readable 
> after cfg_done?);
> - without clearing it "between" frames, the whole screen is always 
> filled with noise, the picture is not visible.
> 
> The rest is at least a bit (ha) speculative:
> 
> As I understand from what the name implies, the hardware sets it to 
> indicate that it has scanned out the frame and is waiting for 
> acknowledgment (clearing) to be able to scan out the next frame. I 
> guess it's a redundant synchronization mechanism that was removed in 
> later iterations of the VOP hardware block.
> 
> I've been trying to see if moving where I clear the bit affects the 
> sort-of-tearing-but-vertical glitches that sometimes happen, especially 
> early on after the system has just booted, but that seems to be 
> completely unrelated pixel clock craziness (the Android kernel runs the 
> screen at 66 fps, interestingly).
> 
> I'm fairly confident that both places are "correct". The reason I'm 
> more on the side of vblank now is that it made logical sense to me when 
> I thought about it more: acknowledging that the frame has been scanned 
> out is a reaction to the frame having been scanned out. It's a 
> consequence of *that* that the acknowledgment is required for the next 
> frame to be drawn.
> 
> Unless we can get the opinion of someone closely familiar with this 
> decade-old hardware, we only have this reasoning to go off of :)

Actually that reasoning was exactly what I was hoping for :-) .
And it actually also makes perfect sense.

I was somehow thinking this needs to be set only when starting output
and not as sort of an Ack.

Could you do a v3 with:
- the findings from above slightly condensed in the commit message
  It's really helpful when someone stumbles onto that commit 10 years
  from now and can get this really helpful explanation from the commit
  message.
- sending it as a _new_ thread
  Having v2 as reply to v1 patches confuses tooling that then can't
  distinguish what is actually part of this v2


Thanks a lot
Heiko