On Mon, Sep 10, 2018 at 09:27:24AM +0200, Boris Brezillon wrote: > Hi Sam, > > On Sat, 8 Sep 2018 22:17:55 +0200 > Sam Ravnborg <sam@xxxxxxxxxxxx> wrote: > > > Hi all. > > > > When working on the DRM driver for Atmel LCDC the first approach > > was to use a MFD driver, that had two sub-drivers: > > - PWM dirver > > - DRM driver > > > > Feedback was that the PWM feature was too small to warrant a MFD driver. > > (There was no consencus on this, but I anyway went ahead). > > > > So the new approch is much simpler (from a code point of view): > > DRM Driver that has one sub-driver > > - PWM driver > > The PWM driver uses registers in the same memory > > range as the DRM driver, so the two drivers uses > > the same regmap. > > > > The PWM driver is located in pwm/ > > The DRM driver is located in gpu/drm/atmel > > The DRM driver uses platform_device_register_data() to > > register the sub-device/driver. > > I have yet to see it work, but I think this is the right way > > to do it. > > > > This all looked fine until reality kicked in. > > > > > > There is the following dependency chain (=> depends on): > > DRM Driver => Panel => Backlight => PWM => DRM Driver > > > > The DRM Driver rely indirectly on the DRM driver, which it not OK. > > > > So the open question is how to fix this dependency challenge? > > > > 1) Drop the generic backlight driver and implement all pwm/backlight > > handling in the driver. > > 2) Re-introduce the MFD driver. > > 3) ? > > > > Any good ideas? > > I keep thinking #2 is the cleanest option. The fact is, the LCDC IP is > actually providing 2 functionalities: a PWM (most of the time driving a > backlight) and a display controller. Really, I don't see why > representing this IP as an MFD is not appropriate, especially since the > HLCDC MFD driver is already in place and can easily be re-used. But can you enable the PWM functionality without the DRM mode? If yes, then I do agree that a PWM driver should be re-introduced (MFD is a bit of a stretch, to me that means "the driver there can do several things on its own", rather than "this is the remaining functionality out of a different driver"). Best regards, Liviu > > What should be adjusted though, is the need for 2 sub-nodes: I think you > can just use a single node and declare #pwm-cells at the top level. > > Regards, > > Boris > > Regards, > > Boris > _______________________________________________ > dri-devel mailing list > dri-devel@xxxxxxxxxxxxxxxxxxxxx > https://lists.freedesktop.org/mailman/listinfo/dri-devel _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
