On Fri, Jun 26, 2015 at 01:54:18PM +0300, Jani Nikula wrote:
> Some 855gm models (at least ThinkPad X40) regressed because of
>
> commit b0cd324faed23d10d66ba6ade66579c681feef6f
> Author: Jani Nikula <[email protected]>
> Date: Wed Nov 12 16:25:43 2014 +0200
>
> drm/i915: don't save/restore backlight hist ctl registers
>
> which tried to make our driver more robust by not blindly saving and
> restoring registers, but it failed to take into account
>
> commit 0eb96d6ed38430b72897adde58f5477a6b71757a
> Author: Jesse Barnes <[email protected]>
> Date: Wed Oct 14 12:33:41 2009 -0700
>
> drm/i915: save/restore BLC histogram control reg across suspend/resume
>
> Fix the regression by enabling hist ctl on gen2.
>
> v2: Improved the comment.
>
> Reported-and-tested-by: Philipp Gesang <[email protected]>
> References: http://mid.gmane.org/20150623222648.GD12335@acheron
> Fixes: b0cd324faed2 ("drm/i915: don't save/restore backlight hist ctl
> registers")
> Cc: Ville Syrjälä <[email protected]>
> Cc: [email protected]
> Acked-by: Chris Wilson <[email protected]>
> Signed-off-by: Jani Nikula <[email protected]>
> ---
> drivers/gpu/drm/i915/i915_reg.h | 1 +
> drivers/gpu/drm/i915/intel_panel.c | 7 +++++++
> 2 files changed, 8 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index fa9ccb87eb66..bf7c08b94088 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -3507,6 +3507,7 @@ enum skl_disp_power_wells {
> #define BLM_POLARITY_PNV (1 << 0) /* pnv only */
>
> #define BLC_HIST_CTL (dev_priv->info.display_mmio_offset + 0x61260)
> +#define BLM_HISTOGRAM_ENABLE (1 << 31)
>
> /* New registers for PCH-split platforms. Safe where new bits show up, the
> * register layout machtes with gen4 BLC_PWM_CTL[12]. */
> diff --git a/drivers/gpu/drm/i915/intel_panel.c
> b/drivers/gpu/drm/i915/intel_panel.c
> index 7d83527f95f7..a55477c59559 100644
> --- a/drivers/gpu/drm/i915/intel_panel.c
> +++ b/drivers/gpu/drm/i915/intel_panel.c
> @@ -907,6 +907,13 @@ static void i9xx_enable_backlight(struct intel_connector
> *connector)
>
> /* XXX: combine this into above write? */
> intel_panel_actually_set_backlight(connector, panel->backlight.level);
> +
> + /*
> + * Needed to enable backlight on some 855gm models.
* BLC_HIST_CTL is 855gm only, but checking for gen2 is
> + * safe, as 855gm is the only gen2 that has backlight.
> + */
I just felt the second sentence lacked a little context to justify
itself.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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