Re: [PATCH] drm/i915: implement MCH pipe underrun prevention for snb/ivb

[Ben Widawsky <ben@bwidawsk.net>]

On Thu, Feb 07, 2013 at 03:23:24PM +0100, Daniel Vetter wrote:
> Some early bios versions seem to ship with the wrong tuning values for
> the MCH, possible resulting in pipe underruns under load. Especially
> on DP outputs this can lead to black screen, since DP really doesn't
> like an occasional whack from an underrun.
> 
> Unfortunately the registers seem to be locked after boot, so the only
> thing we can do is politely point out issues and suggest a BIOS
> upgrade.
> 
> Arthur Runyan pointed us at this issue while discussion DP bugs - thus
> far no confirmation from a bug report yet that it helps. But at least
> some of my machines here have wrong values, so this might be useful in
> understanding bug reports.
> 
> Cc: Runyan, Arthur J <arthur.j.runyan@intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/i915/i915_reg.h |  8 ++++++++
>  drivers/gpu/drm/i915/intel_pm.c | 34 ++++++++++++++++++++++++++++++++++
>  2 files changed, 42 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 8754f91..b3915cf 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -1235,6 +1235,14 @@
>  #define   MAD_DIMM_A_SIZE_SHIFT		0
>  #define   MAD_DIMM_A_SIZE_MASK		(0xff << MAD_DIMM_A_SIZE_SHIFT)
>  
> +/** snb MCH registers for priority tuning */
> +#define MCH_TC_RFP_C0			(MCHBAR_MIRROR_BASE_SNB + 0x4294)
> +#define MCH_TC_RFP_C1			(MCHBAR_MIRROR_BASE_SNB + 0x4694)
> +#define   TC_RFP_OREF_MASK		0xff
> +#define   TC_RFP_OREF_VAL		0xff
> +#define MCH_SSKPD			(MCHBAR_MIRROR_BASE_SNB + 0x5d10)
> +#define   MCH_SSKPD_WM0_MASK		0x3f
> +#define   MCH_SSKPD_WM0_VAL		0xc

According to the bug report I'm reading, there are several valid values,
so I think you should do some more work.

[snip]
-- 
Ben Widawsky, Intel Open Source Technology Center