> Am 28.05.2019 um 17:09 schrieb Adam Ford <aford173@xxxxxxxxx>: > > 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. Well, if this boards needs a factor 4 to be defined, it is IMHO 100 % correct to describe this in the DTS and nowhere else. Like minimum and maximum voltage of a regulator which is also very board specific. Unless it can be figured out automatically. If it turns out later that it can, I would assume the drivers can simply ignore the hint in the DTS? Just my 2cts without knowing details and having tested anything on our DM37 boards. BR, Nikolaus
