Hi Rajeevny, On Tue, May 11, 2021 at 11:41:57PM +0530, rajeevny@xxxxxxxxxxxxxx wrote: > On 01-05-2021 03:08, Doug Anderson wrote: > > On Fri, Apr 30, 2021 at 8:10 AM <rajeevny@xxxxxxxxxxxxxx> wrote: > >> On 30-04-2021 02:33, Doug Anderson wrote: > >> > On Thu, Apr 29, 2021 at 11:04 AM Rob Herring <robh@xxxxxxxxxx> wrote: > >> >> On Mon, Apr 26, 2021 at 11:29:15AM +0530, Rajeev Nandan wrote: > >> >> > Add bindings for DisplayPort aux backlight driver. > >> >> > > >> >> > Changes in v2: > >> >> > - New > >> >> > > >> >> > Signed-off-by: Rajeev Nandan <rajeevny@xxxxxxxxxxxxxx> > >> >> > --- > >> >> > .../bindings/leds/backlight/dp-aux-backlight.yaml | 49 ++++++++++++++++++++++ > >> >> > 1 file changed, 49 insertions(+) > >> >> > create mode 100644 Documentation/devicetree/bindings/leds/backlight/dp-aux-backlight.yaml > >> >> > > >> >> > diff --git a/Documentation/devicetree/bindings/leds/backlight/dp-aux-backlight.yaml b/Documentation/devicetree/bindings/leds/backlight/dp-aux-backlight.yaml > >> >> > new file mode 100644 > >> >> > index 00000000..0fa8bf0 > >> >> > --- /dev/null > >> >> > +++ b/Documentation/devicetree/bindings/leds/backlight/dp-aux-backlight.yaml > >> >> > @@ -0,0 +1,49 @@ > >> >> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) > >> >> > +%YAML 1.2 > >> >> > +--- > >> >> > +$id: http://devicetree.org/schemas/leds/backlight/dp-aux-backlight.yaml# > >> >> > +$schema: http://devicetree.org/meta-schemas/core.yaml# > >> >> > + > >> >> > +title: DisplayPort aux backlight driver bindings > >> >> > + > >> >> > +maintainers: > >> >> > + - Rajeev Nandan <rajeevny@xxxxxxxxxxxxxx> > >> >> > + > >> >> > +description: > >> >> > + Backlight driver to control the brightness over DisplayPort aux channel. > >> >> > + > >> >> > +allOf: > >> >> > + - $ref: common.yaml# > >> >> > + > >> >> > +properties: > >> >> > + compatible: > >> >> > + const: dp-aux-backlight > >> >> > + > >> >> > + ddc-i2c-bus: > >> >> > + $ref: /schemas/types.yaml#/definitions/phandle > >> >> > + description: > >> >> > + A phandle to the system I2C controller connected to the DDC bus used > >> >> > + for the DisplayPort AUX channel. > >> >> > + > >> >> > + enable-gpios: > >> >> > + maxItems: 1 > >> >> > + description: GPIO specifier for backlight enable pin. > >> >> > + > >> >> > + max-brightness: true > >> >> > + > >> >> > +required: > >> >> > + - compatible > >> >> > + - ddc-i2c-bus > >> >> > + > >> >> > +additionalProperties: false > >> >> > + > >> >> > +examples: > >> >> > + - | > >> >> > + backlight { > >> >> > + compatible = "dp-aux-backlight"; > >> >> > + ddc-i2c-bus = <&sn65dsi86_bridge>; > >> >> > + enable-gpios = <&tlmm 12 GPIO_ACTIVE_HIGH>; > >> >> > >> >> So the DDC bus is connected to a backlight and also a panel? This > >> >> binding is not reflecting the h/w, but rather what you want for some > >> >> driver. > >> >> > >> >> There's only one thing here and that's an eDP panel which supports > >> >> backlight control via DP aux channel. You can figure all that out from > >> >> the panel's compatible and/or reading the EDID. > >> >> > >> >> You might also be interested in this thread: > >> >> > >> >> https://lore.kernel.org/lkml/YIKsDtjcIHGNvW0u@xxxxxxxxxxxxxxx/ > >> > > >> > I think Rajeev needs to rework everything anyway as per: > >> > > >> > https://lore.kernel.org/r/87zgxl5qar.fsf@xxxxxxxxx > >> > > >> > ...but you're right that it makes sense not to model the backlight as > >> > a separate node in the device tree. The panel driver can handle > >> > setting up the backlight. > >> > >> It was not a good idea to create a separate backlight driver and use > >> ddc-i2c-bus to get access to DP aux. I am working to move the code > >> to the panel driver and to utilize the new DRM helper functions > >> (drm_edp_backlight_*) Lyude has added [1]. > >> > >> To use these helper functions, the panel driver should have access to the > >> "struct drm_dp_aux *". The simple-panel has a "ddc-i2c-bus" property > >> to give the panel access to the DDC bus and is currently being used to > >> get the EDID from the panel. Can I use the same ddc bus i2c_adapter to get > >> the "struct drm_dp_aux *"? > >> > >> As per the suggestion [2], I get the "struct drm_dp_aux *" from the > >> i2c_adapter of ddc bus (maybe I didn't understand the suggestion correctly), > >> and, it turned out, the way I have implemented is not the right way [3]. > >> So, I am afraid to use the same method in the panel driver. > >> > >> > >> [1] https://lore.kernel.org/dri-devel/871rb5bcf9.fsf@xxxxxxxxx/ > >> [2] https://www.spinics.net/lists/dri-devel/msg295429.html > >> [3] > >> https://lore.kernel.org/dri-devel/20210426111116.4lc3ekxjugjr3oho@xxxxxxxxx/ > > > > So it's definitely up to maintainers, not me. ...but I guess I would > > have expected something like a new property called "ddc-aux-bus". Then > > you'd have to create a new API call called something like > > "of_find_ddc_aux_adapter_by_node()" that would allow you to find it. > > To implement the first suggestion, I can think of the following way > to get the "struct drm_dp_aux" in the panel_simple_probe function: > > - Create a new panel-simple DT property "ddc-aux-bus", a phandle to the > platform device that implements the AUX channel. > > - Create a global list of drm_dp_aux in drm_dp_helper.c. Initialize list > head > in drm_dp_aux_init(), add the drm_dp_aux onto the list in > drm_dp_aux_register(). > Similarly, remove the drm_dp_aux from list in drm_dp_aux_unregister(). > > - Create a new function of_drm_find_dp_aux_by_node() to get the expected > drm_dp_aux from this global list. > > Please let me know your views on this implementation. > > Below is the summary of the changes in drm dp helper: > > --- > > // drm_dp_helper.h > > struct drm_dp_aux { > ... > struct list_head list; > ... > } > > // drm_dp_helper.c > > static DEFINE_MUTEX(dp_aux_lock); > static LIST_HEAD(dp_aux_list); > > static void drm_dp_aux_add(struct drm_dp_aux *aux) > { > mutex_lock(&dp_aux_lock); > list_add_tail(&aux->list, &dp_aux_list); > mutex_unlock(&dp_aux_lock); > } > > static void drm_dp_aux_remove(struct drm_dp_aux *aux) > { > mutex_lock(&dp_aux_lock); > list_del_init(&aux->list); > mutex_unlock(&dp_aux_lock); > } > > #ifdef CONFIG_OF > struct drm_dp_aux *of_drm_find_dp_aux_by_node(struct device_node *np) > { > struct drm_dp_aux *aux; > mutex_lock(&dp_aux_lock); > > list_for_each_entry(aux, &dp_aux_list, list) { > if (aux->dev->of_node == np) { > mutex_unlock(&dp_aux_lock); > return aux; > } > } > > mutex_unlock(&dp_aux_lock); > return NULL; > } > EXPORT_SYMBOL(of_drm_find_dp_aux_by_node); > #endif > > > int drm_dp_aux_init(struct drm_dp_aux *aux) > { > INIT_LIST_HEAD(&aux->list); > ... > } > > int drm_dp_aux_register(struct drm_dp_aux *aux) > { > ... > drm_dp_aux_add(aux); > > return 0; > } > > void drm_dp_aux_unregister(struct drm_dp_aux *aux) > { > drm_dp_aux_remove(aux); > ... > } Overall this seems like a good approach, but there's one unanswered question: what happens if drm_dp_aux_unregister() is called while a panel holds a reference to it ? The drm_dp_aux instances likely need to be reference-counted. > > I guess an alternate way to solve this (I'm not totally sure whether > > it's better or worse) would be to add a function that would walk up > > the chain of parent bridges and ask them for a pointer to the aux bus. > > I definitely haven't thought it all the way through, but I'd imagine > > something like drm_bridge_chain_get_ddc_aux(). This is _probably_ > > better than adding the "ddc-aux-bus" property but it assumes that the > > aux bus is provided by one of our parents. Hrm, looking at this > > briefly, though, I'm not sure how to do it. It doesn't seem possible > > to get the parent bridges from the panel structure. Even if you assume > > that your parent is wrapping you with a panel_bridge it still doesn't > > seem possible? > > > > This probably needs more drm-expertise. -- Regards, Laurent Pinchart
