Re: [RFC 4/5] drm/i915: Enable Intel's HDR backlight interface (only SDR for now)
On Tue, Sep 15, 2020 at 01:29:38PM -0400, Lyude Paul wrote:
> So-recently a bunch of laptops on the market have started using DPCD
> backlight controls instead of the traditional DDI backlight controls.
> Originally we thought we had this handled by adding VESA backlight
> control support to i915, but the story ended up being a lot more
> complicated then that.
>
> Simply put-there's two main backlight interfaces Intel can see in the
> wild. Intel's proprietary HDR backlight interface, and the standard VESA
> backlight interface. Note that many panels have been observed to report
> support for both backlight interfaces, but testing has shown far more
> panels work with the Intel HDR backlight interface at the moment.
> Additionally, the VBT appears to be capable of reporting support for the
> VESA backlight interface but not the Intel HDR interface which needs to
> be probed by setting the right magic OUI.
>
> On top of that however, there's also actually two different variants of
> the Intel HDR backlight interface. The first uses the AUX channel for
> controlling the brightness of the screen in both SDR and HDR mode, and
> the second only uses the AUX channel for setting the brightness level in
> HDR mode - relying on PWM for setting the brightness level in SDR mode.
>
> For the time being we've been using EDIDs to maintain a list of quirks
> for panels that safely do support the VESA backlight interface. Adding
> support for Intel's HDR backlight interface in addition however, should
> finally allow us to auto-detect eDP backlight controls properly so long
> as we probe like so:
>
> * If the panel's VBT reports VESA backlight support, assume it really
> does support it
> * If the panel's VBT reports DDI backlight controls:
> * First probe for Intel's HDR backlight interface
> * If that fails, probe for VESA's backlight interface
> * If that fails, assume no DPCD backlight control
> * If the panel's VBT reports any other backlight type: just assume it
> doesn't have DPCD backlight controls
>
> Note as well that in order for us to make Intel's HDR backlight
> interface appear, we need to start programming the appropriate source
> OUI on the eDP panel as early as possible in the probing process. Note
> that this technically could be done at any time before setting up
> backlight controls, but this way allows us to avoid re-writing it
> multiple times in case we need to use other source-OUI enabled features
> in the future.
>
> Finally, we also make sure to document the registers for this backlight
> interface since eventually, we want to actually implement the full
> interface instead of keeping it in SDR mode.
>
> Signed-off-by: Lyude Paul
> Cc: thay...@noraisin.net
> Cc: Vasily Khoruzhick
> ---
> .../drm/i915/display/intel_display_types.h| 9 +-
> .../drm/i915/display/intel_dp_aux_backlight.c | 384 +++---
> drivers/gpu/drm/i915/display/intel_panel.c| 34 +-
> drivers/gpu/drm/i915/display/intel_panel.h| 4 +
> drivers/gpu/drm/i915/i915_params.c| 2 +-
> 5 files changed, 381 insertions(+), 52 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h
> b/drivers/gpu/drm/i915/display/intel_display_types.h
> index 52a6543df842a..9d540368bac89 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -230,7 +230,14 @@ struct intel_panel {
> struct pwm_state pwm_state;
>
> /* DPCD backlight */
> - u8 pwmgen_bit_count;
> + union {
> + struct {
> + u8 pwmgen_bit_count;
> + } vesa;
> + struct {
> + bool sdr_uses_aux;
> + } intel;
> + } edp;
>
> struct {
> int (*setup)(struct intel_connector *connector, enum
> pipe pipe);
> 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..aa1429302db70 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> @@ -22,10 +22,251 @@
> *
> */
>
> +/*
> + * Laptops with Intel GPUs which have panels that support controlling the
> + * backlight through DP AUX can actually use two different interfaces:
> Intel's
> + * proprietary DP AUX backlight interface, and the standard VESA backlight
> + * interface. Unfortunately, at the time of writing this a lot of laptops
> will
> + * advertise support for the standard VESA backlight interface when they
> + * don't properly support it. However, on these systems the Intel backlight
> + * interface generally does work properly. Additionally, these systems will
> + * usually just indicate that they use PWM backlight controls in their VBIOS
> + * for some reason.
> + */
> +
>
[RFC 4/5] drm/i915: Enable Intel's HDR backlight interface (only SDR for now)
So-recently a bunch of laptops on the market have started using DPCD
backlight controls instead of the traditional DDI backlight controls.
Originally we thought we had this handled by adding VESA backlight
control support to i915, but the story ended up being a lot more
complicated then that.
Simply put-there's two main backlight interfaces Intel can see in the
wild. Intel's proprietary HDR backlight interface, and the standard VESA
backlight interface. Note that many panels have been observed to report
support for both backlight interfaces, but testing has shown far more
panels work with the Intel HDR backlight interface at the moment.
Additionally, the VBT appears to be capable of reporting support for the
VESA backlight interface but not the Intel HDR interface which needs to
be probed by setting the right magic OUI.
On top of that however, there's also actually two different variants of
the Intel HDR backlight interface. The first uses the AUX channel for
controlling the brightness of the screen in both SDR and HDR mode, and
the second only uses the AUX channel for setting the brightness level in
HDR mode - relying on PWM for setting the brightness level in SDR mode.
For the time being we've been using EDIDs to maintain a list of quirks
for panels that safely do support the VESA backlight interface. Adding
support for Intel's HDR backlight interface in addition however, should
finally allow us to auto-detect eDP backlight controls properly so long
as we probe like so:
* If the panel's VBT reports VESA backlight support, assume it really
does support it
* If the panel's VBT reports DDI backlight controls:
* First probe for Intel's HDR backlight interface
* If that fails, probe for VESA's backlight interface
* If that fails, assume no DPCD backlight control
* If the panel's VBT reports any other backlight type: just assume it
doesn't have DPCD backlight controls
Note as well that in order for us to make Intel's HDR backlight
interface appear, we need to start programming the appropriate source
OUI on the eDP panel as early as possible in the probing process. Note
that this technically could be done at any time before setting up
backlight controls, but this way allows us to avoid re-writing it
multiple times in case we need to use other source-OUI enabled features
in the future.
Finally, we also make sure to document the registers for this backlight
interface since eventually, we want to actually implement the full
interface instead of keeping it in SDR mode.
Signed-off-by: Lyude Paul
Cc: thay...@noraisin.net
Cc: Vasily Khoruzhick
---
.../drm/i915/display/intel_display_types.h| 9 +-
.../drm/i915/display/intel_dp_aux_backlight.c | 384 +++---
drivers/gpu/drm/i915/display/intel_panel.c| 34 +-
drivers/gpu/drm/i915/display/intel_panel.h| 4 +
drivers/gpu/drm/i915/i915_params.c| 2 +-
5 files changed, 381 insertions(+), 52 deletions(-)
diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h
b/drivers/gpu/drm/i915/display/intel_display_types.h
index 52a6543df842a..9d540368bac89 100644
--- a/drivers/gpu/drm/i915/display/intel_display_types.h
+++ b/drivers/gpu/drm/i915/display/intel_display_types.h
@@ -230,7 +230,14 @@ struct intel_panel {
struct pwm_state pwm_state;
/* DPCD backlight */
- u8 pwmgen_bit_count;
+ union {
+ struct {
+ u8 pwmgen_bit_count;
+ } vesa;
+ struct {
+ bool sdr_uses_aux;
+ } intel;
+ } edp;
struct {
int (*setup)(struct intel_connector *connector, enum
pipe pipe);
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..aa1429302db70 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
@@ -22,10 +22,251 @@
*
*/
+/*
+ * Laptops with Intel GPUs which have panels that support controlling the
+ * backlight through DP AUX can actually use two different interfaces: Intel's
+ * proprietary DP AUX backlight interface, and the standard VESA backlight
+ * interface. Unfortunately, at the time of writing this a lot of laptops will
+ * advertise support for the standard VESA backlight interface when they
+ * don't properly support it. However, on these systems the Intel backlight
+ * interface generally does work properly. Additionally, these systems will
+ * usually just indicate that they use PWM backlight controls in their VBIOS
+ * for some reason.
+ */
+
#include "intel_display_types.h"
#include "intel_dp_aux_backlight.h"
+#include "intel_panel.h"
+
+/* TODO:
+ * Implement HDR, right now we just implement the bare minimum to bring us
back into SDR mode so we
+ * can make people's backlights
