Hi Sakari, On Tue, Apr 07, 2020 at 09:22:41AM +0300, Sakari Ailus wrote: > On Mon, Apr 06, 2020 at 08:32:34PM +0300, Laurent Pinchart wrote: > > On Mon, Apr 06, 2020 at 07:51:08PM +0300, Sakari Ailus wrote: > > > On Mon, Apr 06, 2020 at 05:42:38PM +0100, Lad Prabhakar wrote: > > > > Modes in the driver are based on xvclk frequency fixed to 24MHz, but where > > > > as the OV5645 sensor can support the xvclk frequency ranging from 6MHz to > > > > 24MHz. So instead making clock-frequency as dt-property just let the > > > > driver enforce the required clock frequency. > > > > > > Even if some current systems where the driver is used are using 24 MHz > > > clock, that doesn't mean there wouldn't be systems using another frequency > > > that the driver does not support right now. > > > > > > The driver really should not set the frequency unless it gets it from DT, > > > but I think the preferred means is to use assigned-clock-rates instead, and > > > not to involve the driver with setting the frequency. > > > > > > Otherwise we'll make it impossible to support other frequencies, at least > > > without more or less random defaults. > > > > We're running in circles here. > > > > As the driver only supports 24MHz at the moment, the frequency should be > > set by the driver, as it's a driver limitation. We can then work on > > supporting additional frequencies, which will require DT to provide a > > list of supported frequencies for the system, but that can be done on > > top. > > I guess it would be possible to use different external clock frequencies on > a sensor in a given system but that seems to be a bit far fetched, to the > extent I've never seen anyone doing that in practice. > > Originally, the driver set the frequency based on the clock-frequency > property. If we're removing that but use a fixed frequency instead, then > how is that going to work going forward when someone adds support for other > frequencies in the driver and has a system requiring that, while there are > some other platforms relying on the driver setting a particular frequency? The standard property for this is link-frequencies, not clock-frequency. Deprecating clock-frequency now paves the way to use the standard property later when/if someone implements support for additional frequencies. > Although, if you're saying that this driver only needs to work with DT that > comes with the kernel and you don't care about DT binary compatibility, > this would be fine. I believe this series to not break backward compatibility, as the driver only works with a 24MHz clock, so I expect all DTs to specify that. -- Regards, Laurent Pinchart
