[Intel-gfx] [PATCH] drm/i915: Don't query PCODE RC6VIDS on platforms not supporting it

[Chris Wilson]

Quoting Imre Deak (2018-02-08 17:41:02)
> On BXT/GLK GEN6_PCODE_READ_RC6VIDS fails with
> MAILBOX_P24C_CC_ILLEGAL_CMD, so don't try to do the query on these
> platforms. Do it only on SNB, IVB and HSW, where we use this command
> anyway for RC6 enabling.
> 
> Based on my tests the command also succeeds on all LLC platforms, but
> it's not clear if it's really supported on those (it returns 0 aka 245mv
> for all RC6 states everywhere except on SNB). BSpec lists the command as
> supported on SKL+ (see P24C_PCODE_MAILBOX_INTERFACE) but that's clearly
> incorrect, since on SKL/KBL the same command ID is used for
> SKL_PCODE_LOAD_HDCP_KEYS. Since the command fails on BXT/GLK, the BSpec
> command list is also incorrect for those platforms (see
> P_CR_P24C_PCODE_MAILBOX_INTERFACE_0_2_0_GTTMMADR).
> 
> I filed a request to update that info in Bspec, but for now let's
> assume a minimal set of platforms where the command is supported.
> 
> Reference: https://bugs.freedesktop.org/show_bug.cgi?id=103337
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c | 24 +++++++++++++++---------
>  1 file changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 2bdce9fea671..8f9045fae3cf 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -1484,9 +1484,12 @@ static int gen6_drpc_info(struct seq_file *m)
>                 gen9_powergate_status = I915_READ(GEN9_PWRGT_DOMAIN_STATUS);
>         }
>  
> -       mutex_lock(&dev_priv->pcu_lock);
> -       sandybridge_pcode_read(dev_priv, GEN6_PCODE_READ_RC6VIDS, &rc6vids);
> -       mutex_unlock(&dev_priv->pcu_lock);
> +       if (INTEL_GEN(dev_priv) <= 7) {
> +               mutex_lock(&dev_priv->pcu_lock);
> +               sandybridge_pcode_read(dev_priv, GEN6_PCODE_READ_RC6VIDS,
> +                                      &rc6vids);
> +               mutex_unlock(&dev_priv->pcu_lock);
> +       }
>  
>         seq_printf(m, "RC1e Enabled: %s\n",
>                    yesno(rcctl1 & GEN6_RC_CTL_RC1e_ENABLE));
> @@ -1542,12 +1545,15 @@ static int gen6_drpc_info(struct seq_file *m)
>         print_rc6_res(m, "RC6+ residency since boot:", GEN6_GT_GFX_RC6p);
>         print_rc6_res(m, "RC6++ residency since boot:", GEN6_GT_GFX_RC6pp);
>  
> -       seq_printf(m, "RC6   voltage: %dmV\n",
> -                  GEN6_DECODE_RC6_VID(((rc6vids >> 0) & 0xff)));
> -       seq_printf(m, "RC6+  voltage: %dmV\n",
> -                  GEN6_DECODE_RC6_VID(((rc6vids >> 8) & 0xff)));
> -       seq_printf(m, "RC6++ voltage: %dmV\n",
> -                  GEN6_DECODE_RC6_VID(((rc6vids >> 16) & 0xff)));
> +       if (INTEL_GEN(dev_priv) <= 7) {

I expect this will confuse gcc-4.4 and it will emit a
maybe-used-uninitialised. I would set rc6vids=0 and then test if
(rc6vids) here.
-Chris