Messages in this thread | | | Date | Tue, 11 May 2021 23:41:57 +0530 | From | rajeevny@codeauro ... | Subject | Re: [v3 1/2] dt-bindings: backlight: add DisplayPort aux backlight |
| |
On 01-05-2021 03:08, Doug Anderson wrote: > Hi, > > On Fri, Apr 30, 2021 at 8:10 AM <rajeevny@codeaurora.org> wrote: >> >> On 30-04-2021 02:33, Doug Anderson wrote: >> > Hi, >> > >> > On Thu, Apr 29, 2021 at 11:04 AM Rob Herring <robh@kernel.org> 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@codeaurora.org> >> >> > --- >> >> > .../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@codeaurora.org> >> >> > + >> >> > +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@orome.fritz.box/ >> > >> > I think Rajeev needs to rework everything anyway as per: >> > >> > https://lore.kernel.org/r/87zgxl5qar.fsf@intel.com >> > >> > ...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. >> > >> > -Doug >> >> 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@intel.com/ >> [2] https://www.spinics.net/lists/dri-devel/msg295429.html >> [3] >> https://lore.kernel.org/dri-devel/20210426111116.4lc3ekxjugjr3oho@maple.lan/ > > 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); ... } ---
Thanks, Rajeev
> 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. > > -Doug
| |