On Mon, Mar 07, 2022 at 04:26:56PM +0100, Max Krummenacher wrote: > On Wed, Mar 2, 2022 at 5:22 PM Marek Vasut <marex@xxxxxxx> wrote: > > > > On 3/2/22 15:21, Maxime Ripard wrote: > > > Hi, > > > > Hi, > > > > > Please try to avoid top posting > Sorry. > > > > > > > On Wed, Feb 23, 2022 at 04:25:19PM +0100, Max Krummenacher wrote: > > >> The goal here is to set the element bus_format in the struct > > >> panel_desc. This is an enum with the possible values defined in > > >> include/uapi/linux/media-bus-format.h. > > >> > > >> The enum values are not constructed in a way that you could calculate > > >> the value from color channel width/shift/mapping/whatever. You rather > > >> would have to check if the combination of color channel > > >> width/shift/mapping/whatever maps to an existing value and otherwise > > >> EINVAL out. > > >> > > >> I don't see the value in having yet another way of how this > > >> information can be specified and then having to write a more > > >> complicated parser which maps the dt data to bus_format. > > > > > > Generally speaking, sending an RFC without explicitly stating what you > > > want a comment on isn't very efficient. > > > > Isn't that what RFC stands for -- Request For Comment ? > > I hoped that the link to the original discussion was enough. > > panel-simple used to have a finite number of hardcoded panels selected > by their compatible. > The following patchsets added a compatible 'panel-dpi' which should > allow to specify the panel in the device tree with timing etc. > https://patchwork.kernel.org/project/dri-devel/patch/20200216181513.28109-6-sam@xxxxxxxxxxxx/ > In the same release cycle part of it got reverted: > https://patchwork.kernel.org/project/dri-devel/patch/20200314153047.2486-3-sam@xxxxxxxxxxxx/ > With this it is no longer possible to set bus_format. > > The explanation what makes the use of a property "data-mapping" not a > suitable way in that revert > is a bit vague. Indeed, but I can only guess. BGR666 in itself doesn't mean much for example. Chances are the DPI interface will use a 24 bit bus, so where is the padding? I think that's what Sam and Laurent were talking about: there wasn't enough information encoded in that property to properly describe the format, hence the revert. > The RFC revert of the revert > https://patchwork.kernel.org/project/dri-devel/patch/20220201110717.3585-1-cniedermaier@xxxxxxxxxxxxxxxxxx/ > tried to get feedback what would be a way forward. This RFC tries the > same by giving a possible solution should > the property name and/or the a bit short strings of the original be > the reason why it is not suitable. > > So the requested comments would be about what was not good enough with > 'data-mapping' and what would be a way forward. > > Especially since in my limited view it is not clear why in panel-lvds > 'data-mapping' is used to state how the bits representing colour are > mapped to the 21 or 28 possible bit position in the LVDS lanes vs. > here where we want to say how the bits representing colour are mapped > to the 16/18/24 lines of the parallel interface would need a different > binding pattern. There's only a few data format in LVDS, so it's ok. A DPI interface is much more free-form, so you need to be a bit more accurate than what is done for LVDS. Maxime
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