The Lyude fde7266fb2f6 change is actually based on Chromium change (https://crrev.com/c/1650325) that fixes the brightness for Samsung Galaxy Chromebook. So currently we have 2 examples that use LSB interpretation and 1 that use MSB.
On Thu, Sep 17, 2020 at 10:55 AM Kevin Chowski <chow...@chromium.org> wrote: > > Apologies for being too vague. To be as precise I can be, here is the > specific code delta I tested: https://crrev.com/c/2406616 . To answer > your other question, the code I tested against is indeed including the > fde7266fb2f6 (despite ostensibly being called 5.4 in my commit > message): our current top-of-tree for our 5.4 branch includes the > intel_dp_aux_calc_max_backlight logic. Further, I'll note that change > is exactly the change which breaks my Pixelbook model: prior to the > change, the max_brightness was hard-coded to 0xFFFF and the math > worked out that it didn't matter that the hardware cared about the MSB > despite the driver code caring about the LSB. > > To answer Ville's question: the fde7266fb2f6 change which fixes one > laptop (I believe Thinkpad X1 extreme Gen 2, from some bug reports I > dug up) and breaks another (Pixelbook); so unfortunately I believe we > need a quirk at least for some laptop. Reading through the copy of the > datasheet I have, it wasn't clear to me which was the correct > interpretation. I'm cc'ing puthik@, who was leaning toward the current > kernel code (caring about LSB) being the correct interpretation. I > believe we have other chromebooks which do rely on LSB functionality, > so unless we can find more examples of laptops wanting MSB it > currently looks like Pixelbook is the outlier. > > On Thu, Sep 17, 2020 at 11:28 AM Jani Nikula > <jani.nik...@linux.intel.com> wrote: > > > > On Thu, 17 Sep 2020, Kevin Chowski <chow...@chromium.org> wrote: > > > We have observed that Google Pixelbook's backlight hardware is > > > interpretting these backlight bits from the most-significant side of the > > > 16 bit word (if DP_EDP_PWMGEN_BIT_COUNT < 16), whereas the driver code > > > assumes the peripheral cares about the least-significant bits. > > > > > > Testing was done from within Chrome OS's build environment when the > > > patch is backported to 5.4 (the version we are newly targeting for the > > > Pixelbook); for the record: > > > $ emerge-eve-kernelnext sys-kernel/chromeos-kernel-5_4 && \ > > > ./update_kernel.sh --remote=$IP > > > > > > I used `/sys/kernel/debug/dri/0/eDP-1/i915_dpcd` on my laptop to verify > > > that the registers were being set according to what the actual hardware > > > expects; I also observe that the backlight is noticeably brighter with > > > this patch. > > > > It's unclear to me what kernel version this is against, and what you've > > actually tested. > > > > Have you tried v5.7 kernel with Lyude's fde7266fb2f6 ("drm/i915: Fix eDP > > DPCD aux max backlight calculations")? > > > > I just want to make sure you've tested with all the relevant fixes > > before adding quirks. > > > > BR, > > Jani. > > > > > > > > Signed-off-by: Kevin Chowski <chow...@chromium.org> > > > --- > > > > > > .../drm/i915/display/intel_dp_aux_backlight.c | 34 +++++++++++++++++++ > > > drivers/gpu/drm/i915/display/intel_quirks.c | 13 +++++++ > > > drivers/gpu/drm/i915/i915_drv.h | 1 + > > > 3 files changed, 48 insertions(+) > > > > > > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c > > > b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c > > > index acbd7eb66cbe3..99c98f217356d 100644 > > > --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c > > > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c > > > @@ -91,6 +91,23 @@ static u32 intel_dp_aux_get_backlight(struct > > > intel_connector *connector) > > > if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT) > > > level = (read_val[0] << 8 | read_val[1]); > > > > > > + if (i915->quirks & QUIRK_SHIFT_EDP_BACKLIGHT_BRIGHTNESS) { > > > + if (!drm_dp_dpcd_readb(&intel_dp->aux, > > > DP_EDP_PWMGEN_BIT_COUNT, > > > + &read_val[0])) { > > > + DRM_DEBUG_KMS("Failed to read DPCD register 0x%x\n", > > > + DP_EDP_PWMGEN_BIT_COUNT); > > > + return 0; > > > + } > > > + // Only bits 4:0 are used, 7:5 are reserved. > > > + read_val[0] = read_val[0] & 0x1F; > > > + if (read_val[0] > 16) { > > > + DRM_DEBUG_KMS("Invalid DP_EDP_PWNGEN_BIT_COUNT > > > 0x%X, expected at most 16\n", > > > + read_val[0]); > > > + return 0; > > > + } > > > + level >>= 16 - read_val[0]; > > > + } > > > + > > > return level; > > > } > > > > > > @@ -106,6 +123,23 @@ intel_dp_aux_set_backlight(const struct > > > drm_connector_state *conn_state, u32 lev > > > struct drm_i915_private *i915 = dp_to_i915(intel_dp); > > > u8 vals[2] = { 0x0 }; > > > > > > + if (i915->quirks & QUIRK_SHIFT_EDP_BACKLIGHT_BRIGHTNESS) { > > > + if (!drm_dp_dpcd_readb(&intel_dp->aux, > > > DP_EDP_PWMGEN_BIT_COUNT, > > > + &vals[0])) { > > > + DRM_DEBUG_KMS("Failed to write aux backlight level: > > > Failed to read DPCD register 0x%x\n", > > > + DP_EDP_PWMGEN_BIT_COUNT); > > > + return; > > > + } > > > + // Only bits 4:0 are used, 7:5 are reserved. > > > + vals[0] = vals[0] & 0x1F; > > > + if (vals[0] > 16) { > > > + DRM_DEBUG_KMS("Failed to write aux backlight level: > > > Invalid DP_EDP_PWNGEN_BIT_COUNT 0x%X, expected at most 16\n", > > > + vals[0]); > > > + return; > > > + } > > > + level <<= (16 - vals[0]) & 0xFFFF; > > > + } > > > + > > > vals[0] = level; > > > > > > /* Write the MSB and/or LSB */ > > > diff --git a/drivers/gpu/drm/i915/display/intel_quirks.c > > > b/drivers/gpu/drm/i915/display/intel_quirks.c > > > index 46beb155d835f..63b27d49b2864 100644 > > > --- a/drivers/gpu/drm/i915/display/intel_quirks.c > > > +++ b/drivers/gpu/drm/i915/display/intel_quirks.c > > > @@ -53,6 +53,16 @@ static void quirk_increase_ddi_disabled_time(struct > > > drm_i915_private *i915) > > > drm_info(&i915->drm, "Applying Increase DDI Disabled quirk\n"); > > > } > > > > > > +/* > > > + * Some eDP backlight hardware uses the most-significant bits of the > > > brightness > > > + * register, so brightness values must be shifted first. > > > + */ > > > +static void quirk_shift_edp_backlight_brightness(struct drm_i915_private > > > *i915) > > > +{ > > > + i915->quirks |= QUIRK_SHIFT_EDP_BACKLIGHT_BRIGHTNESS; > > > + DRM_INFO("Applying shift eDP backlight brightness quirk\n"); > > > +} > > > + > > > struct intel_quirk { > > > int device; > > > int subsystem_vendor; > > > @@ -156,6 +166,9 @@ static struct intel_quirk intel_quirks[] = { > > > /* ASRock ITX*/ > > > { 0x3185, 0x1849, 0x2212, quirk_increase_ddi_disabled_time }, > > > { 0x3184, 0x1849, 0x2212, quirk_increase_ddi_disabled_time }, > > > + > > > + /* Google Pixelbook */ > > > + { 0x591E, 0x8086, 0x2212, quirk_shift_edp_backlight_brightness }, > > > }; > > > > > > void intel_init_quirks(struct drm_i915_private *i915) > > > diff --git a/drivers/gpu/drm/i915/i915_drv.h > > > b/drivers/gpu/drm/i915/i915_drv.h > > > index e4f7f6518945b..cc93bede4fab8 100644 > > > --- a/drivers/gpu/drm/i915/i915_drv.h > > > +++ b/drivers/gpu/drm/i915/i915_drv.h > > > @@ -525,6 +525,7 @@ struct i915_psr { > > > #define QUIRK_PIN_SWIZZLED_PAGES (1<<5) > > > #define QUIRK_INCREASE_T12_DELAY (1<<6) > > > #define QUIRK_INCREASE_DDI_DISABLED_TIME (1<<7) > > > +#define QUIRK_SHIFT_EDP_BACKLIGHT_BRIGHTNESS (1<<8) > > > > > > struct intel_fbdev; > > > struct intel_fbc_work; > > > > -- > > Jani Nikula, Intel Open Source Graphics Center
