Re: [PATCH] drm/i915: Correct sandybrige overclocking

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On Tue, 19 Mar 2013 20:19:56 -0700
Ben Widawsky <ben@bwidawsk.net> wrote:

> Change the gen6+ max delay if the pcode read was successful (not the
> inverse).
> 
> The previous code was all sorts of wrong and has existed since I broke
> it:
> commit 42c0526c930523425ff6edc95b7235ce7ab9308d
> Author: Ben Widawsky <ben@bwidawsk.net>
> Date:   Wed Sep 26 10:34:00 2012 -0700
> 
>     drm/i915: Extract PCU communication
> 
> I added some parentheses for clarity, and I also corrected the debug
> message message to use the mask (wrong before I came along) and added a
> print to show the value we're changing from.
> 
> Looking over the code, I'm not actually sure what we're trying to do. I
> introduced the bug simply by extracting the function not implementing
> anything new. We already set max_delay based on the capabilities
> register (which is what we use elsewhere to determine min and max).
> This would potentially increase it, I suppose? Jesse, I can't find the
> document which explains the definitions of the pcode commands, maybe you
> have it around.
> 
> Based on Jesse's response, this could potentially be for -fixes, or
> stable, or maybe lead to us dropping it entirely. As the current code is
> is, things won't completely break because of the aforementioned
> capabilities register, and in my experimentation, enabling this has no
> effect, it goes from 1100->1100.
> 
> I found this while reviewing Jesse's VLV patches.
> 
> Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
> Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index c30e89a..86729b1 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -2631,9 +2631,11 @@ static void gen6_enable_rps(struct drm_device *dev)
>  	if (!ret) {
>  		pcu_mbox = 0;
>  		ret = sandybridge_pcode_read(dev_priv, GEN6_READ_OC_PARAMS, &pcu_mbox);
> -		if (ret && pcu_mbox & (1<<31)) { /* OC supported */
> +		if (!ret && (pcu_mbox & (1<<31))) { /* OC supported */
> +			DRM_DEBUG_DRIVER("overclocking supported, adjusting frequency max from %dMHz to %dMHz\n",
> +					 ((dev_priv->rps.max_delay & 0xff) * 50),
> +					 ((pcu_mbox & 0xff) * 50));
>  			dev_priv->rps.max_delay = pcu_mbox & 0xff;
> -			DRM_DEBUG_DRIVER("overclocking supported, adjusting frequency max to %dMHz\n", pcu_mbox * 50);
>  		}
>  	} else {
>  		DRM_DEBUG_DRIVER("Failed to set the min frequency\n");

Yeah looks ok.  I don't think I've seen a system where this flag gets
set, but according to the docs this is the right thing to do.

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>

-- 
Jesse Barnes, Intel Open Source Technology Center