I'll defer to Ville & Lyude. I dug up more on the bug report and found that both Thinkpad and Galaxy Chromebook use the same Samsung OLED. So my 2 vs 1 argument is actually not valid. On Fri, Sep 18, 2020 at 10:59 AM Kevin Chowski <chowski@xxxxxxxxxxxx> wrote: > > Apologies once again, some of my emails were bouncing for some > addresses yesterday. Hopefully it was a temporary condition; I'll > continue trying to dig into it on my end if it happens again for this > email. > > Since there's evidence that some models want lsb and some (well, at > least one) want msb, my understanding is that we'll need a quirk one > way or the other (please correct if I'm mistaken). I unfortunately > don't have the ability to test anything other than the Pixelbook, so > if we decide the msb is the "right" way, then I will have to rely on > others to test (and find the OUI of) other models which require lsb. > > I am happy to make any changes requested, but I do not at all have > enough background here to make the decision on whether the msb > functionality deserves the quirk or if the lsb one does. How can I > help you all come to an agreement here? > > * It seems like Ville feels strongly about the msb being the correct > interpretation of the spec. > * It's unclear to me on which side of the fence Lyude falls, I > couldn't pick up a strong opinion in her clarifying question. > * Puthikorn seems to be on the side of lsb being correct, but maybe > was swayed by Ville's argument. > > If no one feels that Ville's argument is not strong in some way, and > we go with that, I will get to work on the requested changes. I am > concerned, though, about changing the default functionality without > testing it widely to find the set of laptops which require the lsb > quirk. I'd appreciate any advice people might have about making this > change safely. > > Thank you for your time, > Kevin > > On Thu, Sep 17, 2020 at 2:11 PM Ville Syrjälä > <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > > > On Thu, Sep 17, 2020 at 09:25:35PM +0300, Ville Syrjälä wrote: > > > On Thu, Sep 17, 2020 at 11:14:43AM -0700, Puthikorn Voravootivat wrote: > > > > 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. > > > > > > "If field 4:0 of the EDP_PWMGEN_BIT_COUNT register represents a value > > > of greater than 8 and the BACKLIGHT_BRIGHTNESS_BYTE_COUNT bit > > > is cleared to 0, only the 8 MSB of the brightness control value can be > > > controlled. > > > (See Note below.) > > > Assigned bits are allocated to the MSB of the enabled register > > > combination." > > > > > > I think that's pretty clear the assigned bits are supposed to be > > > msb aligned. > > > > I guess there's some email issues happening, but just to clarify: > > > > When the spec says MSB in caps here it clearly means > > "most significant-bit(s)" since otherwise "8 MSB" would not make > > any sense in the context of a 2 byte value. > > > > Granted the spec is crap here since "Table 1-1: Acronyms and > > Initialism" does claim "MSB" should be byte(s) and "msb" bit(s). > > > > Also I can't imagine anyone would allocate the bits starting > > from the lsb when the whole thing is clearly supposed to be a > > 16bit big endian integer. So with >8 assigned bits you'd end > > up with crazy stuff like this: > > > > [ 7 ... 0 ][7 ... 0] > > [ 8 MSB ][XXXX][N LSB] > > > > so you couldn't even treat the value as a regular big endian > > thing. Instead, if you squint a bit, it now looks like a funky > > little endian value. So we're deep into some mixed endian land > > where nothing makes sense anymore. > > > > Anyways I think the code should simply do this to match the spec: > > u16 value = brightness << (16 - num_assigned_bits); > > val[0] = value >> 8; > > val[1] = value & 0xff; > > > > > > > > > > > > > > > > > > > On Thu, Sep 17, 2020 at 10:55 AM Kevin Chowski <chowski@xxxxxxxxxxxx> 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.nikula@xxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > On Thu, 17 Sep 2020, Kevin Chowski <chowski@xxxxxxxxxxxx> 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 <chowski@xxxxxxxxxxxx> > > > > > > > --- > > > > > > > > > > > > > > .../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 > > > > > > -- > > > Ville Syrjälä > > > Intel > > > _______________________________________________ > > > Intel-gfx mailing list > > > Intel-gfx@xxxxxxxxxxxxxxxxxxxxx > > > https://lists.freedesktop.org/mailman/listinfo/intel-gfx > > > > -- > > Ville Syrjälä > > Intel _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
