On 17 August 2015 at 16:15, Liviu Dudau <Liviu.Dudau@xxxxxxx> wrote: > On Sun, Aug 16, 2015 at 09:56:33AM +0100, Emil Velikov wrote: >> Hi Liviu, > > Hi Emil, > >> >> On 5 August 2015 at 15:28, Liviu Dudau <Liviu.Dudau@xxxxxxx> wrote: >> > The HDLCD controller is a display controller that supports resolutions >> > up to 4096x4096 pixels. It is present on various development boards >> > produced by ARM Ltd and emulated by the latest Fast Models from the >> > company. >> > >> I believe there is a unofficial requirement(?) for new drm drivers to >> use atomic modesetting. Not 100% sure on this one though. The >> following drivers: tegra, msm, rcar-du, i915, and Daniel's blog [1] >> [2] cat provide some information on the topic. > > I am also interested to know if this is a requirement or not. > Thanks for the pointers, I will review them again to see if I did miss > anything. I remember reading them at the beginning of the year but probably > the Christmas haze did not clear enough when I did. > There was a similar question from the freescale dcu people [1]. I believe that the answer still applies. [1] http://lists.freedesktop.org/archives/dri-devel/2015-March/078689.html >> >> The driver seems to has has a bit of dead code guarded by >> HDLCD_*_UNDERRUN. Perhaps these macros should become build or runtime >> switch(es) ? > > There is a comment in hdlcd_drv.h explaining what HDLCD_SHOW_UNDERRUN can > be used for. As for HDLCD_COUNT_BUFFERUNDERRUNS, you are right, it's dead > code from the earlier debugging code that got removed before submission. > I will correct that. > I haven't seen other drm drivers follow the "set a macro that is documented in a header and rebuild" approach. Devs either add a CONFIG option for it, or expose it as a module parameter. IIRC the nouveau driver does even more - it enables the underrun machinery unconditionally. >> >> Most DRM drivers do not threat dma, bus_error, vsync and/or underrun >> interrupts as debug functionality. They are of limited use in this >> driver, presently, yet the CONFIG_DEBUG_FS guard seems a bit strange >> imho. > > The HDLCD device has only 1 interrupt that can fire and there is no other > way to show the reason for the interrupt in the driver. It was useful when > debugging underruns and/or vsync issues so I thought it might be useful > to keep around. Putting it the other way: if you are going to use this device > and the image is not completely rendered I would not be able to give you > support to figure out what went wrong without this debugging information. > With this in place I can tell the difference between a busy system vs one > where the interrupt latency is large. > Out of curiosity - are there any implications/side-effects from having these enabled ? Thanks, Emil -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
