On Tue, May 28, 2019 at 10:53 AM Tomi Valkeinen <tomi.valkeinen@xxxxxx> wrote: > > Hi, > > On 28/05/2019 18:09, Adam Ford wrote: > > On Tue, May 28, 2019 at 4:11 AM Tomi Valkeinen <tomi.valkeinen@xxxxxx> wrote: > >> > >> Hi, > >> > >> On 10/05/2019 22:42, Adam Ford wrote: > >>> Currently the source code is compiled using hard-coded values > >>> from CONFIG_OMAP2_DSS_MIN_FCK_PER_PCK. This patch allows this > >>> clock divider value to be moved to the device tree and be changed > >>> without having to recompile the kernel. > >>> > >>> Signed-off-by: Adam Ford <aford173@xxxxxxxxx> > >> > >> I understand why you want to do this, but I'm not sure it's a good idea. > >> It's really something the driver should figure out, and if we add it to > >> the DT, it effectively becomes an ABI. > >> > >> That said... I'm not sure how good of a job the driver could ever do, as > >> it can't know the future scaling needs of the userspace at the time it > >> is configuring the clock. And so, I'm not nacking this patch, but I > >> don't feel very good about this patch... > >> > >> The setting also affects all outputs (exluding venc), which may not be > >> what the user wants. Then again, I think this setting is really only > >> needed on OMAP2 & 3, which have only a single output. But that's the > >> same with the current kconfig option, of course. > >> > >> So, the current CONFIG_OMAP2_DSS_MIN_FCK_PER_PCK is an ugly hack, in my > >> opinion, and moving it to DT makes it a worse hack =). But I don't have > >> any good suggestions either. > > > > As it stands the Logic PD OMAP35 and AM37/DM37 boards (SOM-LV and > > Torpedo) require this to be hard coded to 4 or it hangs during start. > > This is the case for all versions 4.2+. I haven't tested it with > > older stuff. Tony has a DM3730 Torpedo kit and reported the hanging > > issue to me. I told him to set that value to 4 to make it not hang. > > He asked that I move it to the DT to avoid custom kernels. I agree > > it's a hack, but if it's create a customized defconfig file for 4 > > boards or modify the device tree, it seems like the device tree > > approach is less intrusive. > > Ok, well, I think that's a separate thing from its intended use. The > point of the kconfig option is to ensure that the fclk/pclk ratio stays > under a certain number to allow enough scaling range. It should never > affect a basic non-scaling use case, unless you set it to a too high > value, which prevents finding any pclk. > > Has anyone debugged why the hang is happening? I tried debugging this years ago, and I was told to use the CONFIG_OMAP2_DSS_MIN_FCK_PER_PCK. > > If we can't fix the bug itself, rather than adding a DT option, we could > change add a min_fck_per_pck field (as you do), keep the kconfig option, > and set the min_fck_per_pck based on the kconfig option, _or_ in case of > those affected SoCs, set the min_fck_per_pck even without the kconfig > option. I am just curious if anyone else sees this. If nobody is using this hack, I wonder how much of the impact it will be. I'm trying trying to get my board to boot without hanging without creating a custom defconfig. adam > > Tomi > > -- > Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. > Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
