[Intel-gfx] [PATCH 1/4] drm/i915/skl: Fix has_ipc on skl and document WaDisableIPC.

[Mahesh Kumar]

Hi,


On Friday 29 September 2017 12:21 AM, Rodrigo Vivi wrote:
> According to Spec for SKL+: "Isochronous Priority Control.
> If enabled, Display sends demoted requests once the transition
> watermark is reached. If transition watermark is not enabled,
> Display sends demoted requests when the display buffer is full."
>
> The commit 'e57f1c02155f ("drm/i915/gen9+: Add has_ipc flag in
> device info structure")' introduced that as gen9+ but missing many
> SKL Skus.
>
> I believe the reason for that is Spec also mentions workarounds for
> SKL-ALL: "IPC (Isoch Priority Control) may cause underflows
> WA: Do not enable IPC in register ARB_CTL2"
yes, it was intentional as you correctly pointed out WA #0477.
>
> It seems lame to add the feature and forever disable it,
> but it will avoid a mistake of enabling it when we are reorganizing
> the feature definitions on i915_pci.c later.
sounds Good,
>
> It will also allow us to probably extend that workaround for
> other platforms.
>
> Cc: Mahesh Kumar <mahesh1.kumar at intel.com>
> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> ---
>   drivers/gpu/drm/i915/i915_pci.c | 1 +
>   drivers/gpu/drm/i915/intel_pm.c | 6 ++++++
>   2 files changed, 7 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_pci.c b/drivers/gpu/drm/i915/i915_pci.c
> index da60866b6628..df751a152057 100644
> --- a/drivers/gpu/drm/i915/i915_pci.c
> +++ b/drivers/gpu/drm/i915/i915_pci.c
> @@ -426,6 +426,7 @@ static const struct intel_device_info intel_cherryview_info __initconst = {
>   	.platform = INTEL_SKYLAKE, \
>   	.has_csr = 1, \
>   	.has_guc = 1, \
> +	.has_ipc = 1, \
>   	.ddb_size = 896
>   
>   static const struct intel_device_info intel_skylake_gt1_info __initconst = {
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 52c4c194aa51..ede871b7982e 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -5828,6 +5828,12 @@ void intel_enable_ipc(struct drm_i915_private *dev_priv)
>   {
>   	u32 val;
>   
> +	/* Display WA #0477 WaDisableIPC: skl */
> +	if (IS_SKYLAKE(dev_priv)) {
> +		dev_priv->ipc_enabled = false;
> +		return;
> +	}
> +
looks good to me.
Reviewed-by: Mahesh Kumar <mahesh1.kumar at intel.com>
-Mahesh
>   	val = I915_READ(DISP_ARB_CTL2);
>   
>   	if (dev_priv->ipc_enabled)

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