Re: [PATCH v5 1/6] drm/vc4: Avoid using vrefresh==0 mode in DSI htotal math.

[Boris Brezillon]

Le Fri, 04 Aug 2017 14:15:56 -0700,
Eric Anholt  a écrit :

> Boris Brezillon  writes:
> 
> > On Tue, 18 Jul 2017 14:05:05 -0700
> > Eric Anholt  wrote:
> >  
> >> The incoming mode might have a missing vrefresh field if it came from
> >> drmModeSetCrtc(), which the kernel is supposed to calculate using
> >> drm_mode_vrefresh().  We could either use that or the adjusted_mode's
> >> original vrefresh value.
> >> 
> >> However, we can maintain a more exact vrefresh value (not just the
> >> integer approximation), by scaling by the ratio of our clocks.
> >> 
> >> v2: Use math suggested by Andrzej Hajda instead.
> >> 
> >> Signed-off-by: Eric Anholt 
> >> ---
> >>  drivers/gpu/drm/vc4/vc4_dsi.c | 3 ++-
> >>  1 file changed, 2 insertions(+), 1 deletion(-)
> >> 
> >> diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
> >> index 629d372633e6..57213f4e3c72 100644
> >> --- a/drivers/gpu/drm/vc4/vc4_dsi.c
> >> +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
> >> @@ -866,7 +866,8 @@ static bool vc4_dsi_encoder_mode_fixup(struct 
> >> drm_encoder *encoder,
> >>adjusted_mode->clock = pixel_clock_hz / 1000 + 1;
> >>  
> >>/* Given the new pixel clock, adjust HFP to keep vrefresh the same. */
> >> -  adjusted_mode->htotal = pixel_clock_hz / (mode->vrefresh * 
> >> mode->vtotal);
> >> +  adjusted_mode->htotal = (pixel_clock_hz / 1000 * mode->htotal /
> >> +   mode->clock);  
> >
> > Hm, I'm not sure I understand this. Shouldn't we have something like:
> >
> > adjusted_mode->htotal = (adjusted_mode->clock * mode->htotal) /
> > mode->clock;
> >
> > Is there a reason for doing '+ 1' when you calculate the adjusted
> > pixel clock rate but not here?  
> 
> We're actually expecting to get within epsilon of pixel_clock_hz, but we
> have to bump our clk_set_rate() to a higher value because the clock
> driver will give you a bad divider if you ask for anything less than the
> rate it can provide.
> 
> How about I don't increment the adjusted_mode->clock (since it'll be
> userspace visible I think), and instead move that and the "Round up"
> comment to the clk_set_rate()?

Sounds good.

Re: [PATCH v5 1/6] drm/vc4: Avoid using vrefresh==0 mode in DSI htotal math.

[Boris Brezillon]

Le Fri, 04 Aug 2017 14:15:56 -0700,
Eric Anholt  a écrit :

> Boris Brezillon  writes:
> 
> > On Tue, 18 Jul 2017 14:05:05 -0700
> > Eric Anholt  wrote:
> >  
> >> The incoming mode might have a missing vrefresh field if it came from
> >> drmModeSetCrtc(), which the kernel is supposed to calculate using
> >> drm_mode_vrefresh().  We could either use that or the adjusted_mode's
> >> original vrefresh value.
> >> 
> >> However, we can maintain a more exact vrefresh value (not just the
> >> integer approximation), by scaling by the ratio of our clocks.
> >> 
> >> v2: Use math suggested by Andrzej Hajda instead.
> >> 
> >> Signed-off-by: Eric Anholt 
> >> ---
> >>  drivers/gpu/drm/vc4/vc4_dsi.c | 3 ++-
> >>  1 file changed, 2 insertions(+), 1 deletion(-)
> >> 
> >> diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
> >> index 629d372633e6..57213f4e3c72 100644
> >> --- a/drivers/gpu/drm/vc4/vc4_dsi.c
> >> +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
> >> @@ -866,7 +866,8 @@ static bool vc4_dsi_encoder_mode_fixup(struct 
> >> drm_encoder *encoder,
> >>adjusted_mode->clock = pixel_clock_hz / 1000 + 1;
> >>  
> >>/* Given the new pixel clock, adjust HFP to keep vrefresh the same. */
> >> -  adjusted_mode->htotal = pixel_clock_hz / (mode->vrefresh * 
> >> mode->vtotal);
> >> +  adjusted_mode->htotal = (pixel_clock_hz / 1000 * mode->htotal /
> >> +   mode->clock);  
> >
> > Hm, I'm not sure I understand this. Shouldn't we have something like:
> >
> > adjusted_mode->htotal = (adjusted_mode->clock * mode->htotal) /
> > mode->clock;
> >
> > Is there a reason for doing '+ 1' when you calculate the adjusted
> > pixel clock rate but not here?  
> 
> We're actually expecting to get within epsilon of pixel_clock_hz, but we
> have to bump our clk_set_rate() to a higher value because the clock
> driver will give you a bad divider if you ask for anything less than the
> rate it can provide.
> 
> How about I don't increment the adjusted_mode->clock (since it'll be
> userspace visible I think), and instead move that and the "Round up"
> comment to the clk_set_rate()?

Sounds good.

Re: [PATCH v5 1/6] drm/vc4: Avoid using vrefresh==0 mode in DSI htotal math.

[Eric Anholt]

Boris Brezillon  writes:

> On Tue, 18 Jul 2017 14:05:05 -0700
> Eric Anholt  wrote:
>
>> The incoming mode might have a missing vrefresh field if it came from
>> drmModeSetCrtc(), which the kernel is supposed to calculate using
>> drm_mode_vrefresh().  We could either use that or the adjusted_mode's
>> original vrefresh value.
>> 
>> However, we can maintain a more exact vrefresh value (not just the
>> integer approximation), by scaling by the ratio of our clocks.
>> 
>> v2: Use math suggested by Andrzej Hajda instead.
>> 
>> Signed-off-by: Eric Anholt 
>> ---
>>  drivers/gpu/drm/vc4/vc4_dsi.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
>> index 629d372633e6..57213f4e3c72 100644
>> --- a/drivers/gpu/drm/vc4/vc4_dsi.c
>> +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
>> @@ -866,7 +866,8 @@ static bool vc4_dsi_encoder_mode_fixup(struct 
>> drm_encoder *encoder,
>>  adjusted_mode->clock = pixel_clock_hz / 1000 + 1;
>>  
>>  /* Given the new pixel clock, adjust HFP to keep vrefresh the same. */
>> -adjusted_mode->htotal = pixel_clock_hz / (mode->vrefresh * 
>> mode->vtotal);
>> +adjusted_mode->htotal = (pixel_clock_hz / 1000 * mode->htotal /
>> + mode->clock);
>
> Hm, I'm not sure I understand this. Shouldn't we have something like:
>
>   adjusted_mode->htotal = (adjusted_mode->clock * mode->htotal) /
>   mode->clock;
>
> Is there a reason for doing '+ 1' when you calculate the adjusted
> pixel clock rate but not here?

We're actually expecting to get within epsilon of pixel_clock_hz, but we
have to bump our clk_set_rate() to a higher value because the clock
driver will give you a bad divider if you ask for anything less than the
rate it can provide.

How about I don't increment the adjusted_mode->clock (since it'll be
userspace visible I think), and instead move that and the "Round up"
comment to the clk_set_rate()?


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Re: [PATCH v5 1/6] drm/vc4: Avoid using vrefresh==0 mode in DSI htotal math.

[Eric Anholt]

Boris Brezillon  writes:

> On Tue, 18 Jul 2017 14:05:05 -0700
> Eric Anholt  wrote:
>
>> The incoming mode might have a missing vrefresh field if it came from
>> drmModeSetCrtc(), which the kernel is supposed to calculate using
>> drm_mode_vrefresh().  We could either use that or the adjusted_mode's
>> original vrefresh value.
>> 
>> However, we can maintain a more exact vrefresh value (not just the
>> integer approximation), by scaling by the ratio of our clocks.
>> 
>> v2: Use math suggested by Andrzej Hajda instead.
>> 
>> Signed-off-by: Eric Anholt 
>> ---
>>  drivers/gpu/drm/vc4/vc4_dsi.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
>> index 629d372633e6..57213f4e3c72 100644
>> --- a/drivers/gpu/drm/vc4/vc4_dsi.c
>> +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
>> @@ -866,7 +866,8 @@ static bool vc4_dsi_encoder_mode_fixup(struct 
>> drm_encoder *encoder,
>>  adjusted_mode->clock = pixel_clock_hz / 1000 + 1;
>>  
>>  /* Given the new pixel clock, adjust HFP to keep vrefresh the same. */
>> -adjusted_mode->htotal = pixel_clock_hz / (mode->vrefresh * 
>> mode->vtotal);
>> +adjusted_mode->htotal = (pixel_clock_hz / 1000 * mode->htotal /
>> + mode->clock);
>
> Hm, I'm not sure I understand this. Shouldn't we have something like:
>
>   adjusted_mode->htotal = (adjusted_mode->clock * mode->htotal) /
>   mode->clock;
>
> Is there a reason for doing '+ 1' when you calculate the adjusted
> pixel clock rate but not here?

We're actually expecting to get within epsilon of pixel_clock_hz, but we
have to bump our clk_set_rate() to a higher value because the clock
driver will give you a bad divider if you ask for anything less than the
rate it can provide.

How about I don't increment the adjusted_mode->clock (since it'll be
userspace visible I think), and instead move that and the "Round up"
comment to the clk_set_rate()?


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Re: [PATCH v5 1/6] drm/vc4: Avoid using vrefresh==0 mode in DSI htotal math.

[Boris Brezillon]

On Tue, 18 Jul 2017 14:05:05 -0700
Eric Anholt  wrote:

> The incoming mode might have a missing vrefresh field if it came from
> drmModeSetCrtc(), which the kernel is supposed to calculate using
> drm_mode_vrefresh().  We could either use that or the adjusted_mode's
> original vrefresh value.
> 
> However, we can maintain a more exact vrefresh value (not just the
> integer approximation), by scaling by the ratio of our clocks.
> 
> v2: Use math suggested by Andrzej Hajda instead.
> 
> Signed-off-by: Eric Anholt 
> ---
>  drivers/gpu/drm/vc4/vc4_dsi.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
> index 629d372633e6..57213f4e3c72 100644
> --- a/drivers/gpu/drm/vc4/vc4_dsi.c
> +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
> @@ -866,7 +866,8 @@ static bool vc4_dsi_encoder_mode_fixup(struct drm_encoder 
> *encoder,
>   adjusted_mode->clock = pixel_clock_hz / 1000 + 1;
>  
>   /* Given the new pixel clock, adjust HFP to keep vrefresh the same. */
> - adjusted_mode->htotal = pixel_clock_hz / (mode->vrefresh * 
> mode->vtotal);
> + adjusted_mode->htotal = (pixel_clock_hz / 1000 * mode->htotal /
> +  mode->clock);

Hm, I'm not sure I understand this. Shouldn't we have something like:

adjusted_mode->htotal = (adjusted_mode->clock * mode->htotal) /
mode->clock;

Is there a reason for doing '+ 1' when you calculate the adjusted
pixel clock rate but not here?

>   adjusted_mode->hsync_end += adjusted_mode->htotal - mode->htotal;
>   adjusted_mode->hsync_start += adjusted_mode->htotal - mode->htotal;
>  

Re: [PATCH v5 1/6] drm/vc4: Avoid using vrefresh==0 mode in DSI htotal math.

[Boris Brezillon]

On Tue, 18 Jul 2017 14:05:05 -0700
Eric Anholt  wrote:

> The incoming mode might have a missing vrefresh field if it came from
> drmModeSetCrtc(), which the kernel is supposed to calculate using
> drm_mode_vrefresh().  We could either use that or the adjusted_mode's
> original vrefresh value.
> 
> However, we can maintain a more exact vrefresh value (not just the
> integer approximation), by scaling by the ratio of our clocks.
> 
> v2: Use math suggested by Andrzej Hajda instead.
> 
> Signed-off-by: Eric Anholt 
> ---
>  drivers/gpu/drm/vc4/vc4_dsi.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
> index 629d372633e6..57213f4e3c72 100644
> --- a/drivers/gpu/drm/vc4/vc4_dsi.c
> +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
> @@ -866,7 +866,8 @@ static bool vc4_dsi_encoder_mode_fixup(struct drm_encoder 
> *encoder,
>   adjusted_mode->clock = pixel_clock_hz / 1000 + 1;
>  
>   /* Given the new pixel clock, adjust HFP to keep vrefresh the same. */
> - adjusted_mode->htotal = pixel_clock_hz / (mode->vrefresh * 
> mode->vtotal);
> + adjusted_mode->htotal = (pixel_clock_hz / 1000 * mode->htotal /
> +  mode->clock);

Hm, I'm not sure I understand this. Shouldn't we have something like:

adjusted_mode->htotal = (adjusted_mode->clock * mode->htotal) /
mode->clock;

Is there a reason for doing '+ 1' when you calculate the adjusted
pixel clock rate but not here?

>   adjusted_mode->hsync_end += adjusted_mode->htotal - mode->htotal;
>   adjusted_mode->hsync_start += adjusted_mode->htotal - mode->htotal;
>