Re: [PATCH v11 1/7] drm/i915/gen6+: Return -EINVAL on invalid pcode commands

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

On Thu, Aug 11, 2016 at 03:54:30PM -0400, Lyude wrote:
> In order to add proper support for the SAGV, we need to be able to know
> what the cause of a failure to change the SAGV through the pcode mailbox
> was. The reasoning for this is that some very early pre-release Skylake
> machines don't actually allow you to control the SAGV on them, and
> indicate an invalid mailbox command was sent.
> 
> This also might come in handy in the future for debugging.
> 
> Signed-off-by: Lyude <cpaul@redhat.com>
> Cc: Matt Roper <matthew.d.roper@intel.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: stable@vger.kernel.org
> ---
>  drivers/gpu/drm/i915/i915_reg.h |  1 +
>  drivers/gpu/drm/i915/intel_pm.c | 10 ++++++++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index da82744..73b3d4d 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -7121,6 +7121,7 @@ enum {
>  #define VLV_MEDIA_C0_COUNT			_MMIO(0x13811C)
>  
>  #define GEN6_PCODE_MAILBOX			_MMIO(0x138124)
> +#define   GEN6_PCODE_INVALID_CMD		(1<<0)

It doesn't work quite like that. Instead the low 8 bits will contian
the error code, iff pcode has cleared the "READY" bit:

snb-ivb docs say:
00h MAILBOX_GTDRIVER_CC_SUCCESS
01h MAILBOX_GTDRIVER_CC_ILLEGAL_CMD
02h MAILBOX_GTDRIVER_CC_MIN_FREQUENCY_TABLE_GT_RATIO_OUT_OF_RANGE
03h MAILBOX_GTDRIVER_CC_TIMEOUT
FFh MAILBOX_GTDRIVER_CC_UNIMPLEMENTED_CMD

hsw-bdw docs say:
00h SUCCESS
01h ILLEGAL_CMD
02h TIMEOUT
03h ILLEGAL_DATA
10h MIN_FREQUENCY_TABLE_GT_RATIO_OUT_OF_RANGE

skl docs say:
00h SUCCESS
01h ILLEGAL_CMD
02h TIMEOUT
03h ILLEGAL_DATA

So looks like 02h and 03h will need to be interpreted in two different
ways depending on the platform. Assuming we want to decode the error
into a a human readable form for dmesg.

>  #define   GEN6_PCODE_READY			(1<<31)
>  #define	  GEN6_PCODE_WRITE_RC6VIDS		0x4
>  #define	  GEN6_PCODE_READ_RC6VIDS		0x5
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 99014d7..8752730 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -7674,6 +7674,11 @@ int sandybridge_pcode_read(struct drm_i915_private *dev_priv, u32 mbox, u32 *val
>  	*val = I915_READ_FW(GEN6_PCODE_DATA);
>  	I915_WRITE_FW(GEN6_PCODE_DATA, 0);
>  
> +	if (I915_READ_FW(GEN6_PCODE_MAILBOX) & GEN6_PCODE_INVALID_CMD) {
> +		DRM_DEBUG_DRIVER("warning: pcode (read) mailbox access indicated invalid command\n");
> +		return -EINVAL;
> +	}
> +
>  	return 0;
>  }
>  
> @@ -7704,6 +7709,11 @@ int sandybridge_pcode_write(struct drm_i915_private *dev_priv,
>  
>  	I915_WRITE_FW(GEN6_PCODE_DATA, 0);
>  
> +	if (I915_READ_FW(GEN6_PCODE_MAILBOX) & GEN6_PCODE_INVALID_CMD) {
> +		DRM_DEBUG_DRIVER("warning: pcode (write) mailbox access indicated invalid command\n");
> +		return -EINVAL;
> +	}
> +
>  	return 0;
>  }
>  
> -- 
> 2.7.4

-- 
Ville Syrjälä
Intel OTC