Re: [PATCH v4 0/6] Check pixel clock when setting mode

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Feb 02, 2016 at 03:16:37PM +0200, Mika Kahola wrote:
> From EDID we can read and request higher pixel clock than
> our HW can support. This set of patches add checks if
> requested pixel clock is lower than the one supported by the HW.
> The requested mode is discarded if we cannot support the requested
> pixel clock. For example for Cherryview
> 
> 'cvt 2560 1600 60' gives
> 
> # 2560x1600 59.99 Hz (CVT 4.10MA) hsync: 99.46 kHz; pclk: 348.50 MHz
> Modeline "2560x1600_60.00"  348.50  2560 2760 3032 3504  1600 1603 1609 1658 -hsync +vsync
> 
> where pixel clock 348.50 MHz is higher than the supported 304 MHz.
> 
> The missing mode validity checks for DisplayPort, HDMI, DP-MST, SDVO, CRT, and TV.
> 
> V2:
> - The maximum DOT clock frequency is added to debugfs i915_frequency_info.
> - max dotclock cached in dev_priv structure
> - moved computation of max dotclock to 'intel_display.c'
> 
> V3:
> - intel_update_max_dotclk() renamed as intel_compute_max_dotclk()
> - for GEN9 and above the max dotclock frequency is equal to CD clock
>   frequency
> - for older generations the dot clock frequency is limited to 90% of the
>   CD clock frequency
> - For Cherryview the dot clock is limited to 95% of CD clock frequency
> - for GEN2/3 the maximum dot clock frequency is limited to 90% of the
>   2X CD clock frequency as we have on option to use double wide mode
> - cleanup
> 
> V4:
> - renaming of max_dotclk as max_dotclk_freq in dev_priv (i915_drv.h)
>   caused changes to all patches in my series even though some of them has
>   been r-b'd by Ville
> - for consistency the max_pixclk variable is renamed as max_dotclk throughout
>   the whole series
> 
> Mika Kahola (6):
>   drm/i915: DisplayPort pixel clock check
>   drm/i915: HDMI pixel clock check
>   drm/i915: DisplayPort-MST pixel clock check
>   drm/i915: SDVO pixel clock check
>   drm/i915: CRT pixel clock check
>   drm/i915: TV pixel clock check

I think I've r-b'd these in the past, but just in case I had another
look and it still looks OK to me. So, for the series:
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Now, apparently there are some actual bugs out there that could be
fixed by this. Eg:
https://bugzilla.redhat.com/show_bug.cgi?id=1279797

We had one bug in fdo too, but somehow that got closed before we added
any of the relevant checks. I think it was this one:
https://bugs.freedesktop.org/show_bug.cgi?id=85621

I'd be tempted to put cc:stable on this stuff actually, to get those
bugs fixed. Looks max_dotclock_freq got merged in 4.4 so we can't
backport beyond that.

> 
>  drivers/gpu/drm/i915/intel_crt.c    | 4 ++++
>  drivers/gpu/drm/i915/intel_dp.c     | 3 ++-
>  drivers/gpu/drm/i915/intel_dp_mst.c | 5 +++++
>  drivers/gpu/drm/i915/intel_hdmi.c   | 8 ++++++++
>  drivers/gpu/drm/i915/intel_sdvo.c   | 4 ++++
>  drivers/gpu/drm/i915/intel_tv.c     | 4 ++++
>  6 files changed, 27 insertions(+), 1 deletion(-)
> 
> -- 
> 1.9.1
> 
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-- 
Ville Syrjälä
Intel OTC
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