Hi Maxime, Le Wed 02 Jul 25, 13:36, Maxime Ripard a écrit : > On Tue, Jul 01, 2025 at 10:11:24PM +0200, Paul Kocialkowski wrote: > > The DE mixer clock is currently set to run at 150 MHz, while the > > Allwinner BSP configures it at 300 MHz and other platforms typically > > run at 297 MHz. > > > > 150 MHz appears to be enough given the restricted graphics capabilities > > of the SoC (with a work area of only 1024x1024). However it typically > > causes the DE clock to be parented to the periph0 pll instead of the > > video PLL. > > > > While this should generally not be a concern, it appears (based on > > experimentation) that both the DE and TCON clocks need to be parented > > to the same PLL for these units to work. While we cannot represent this > > constraint in the clock driver, it appears that the TCON clock will > > often get parented to the video pll (typically running at 297 MHz for > > the CSI units needs), for instance when driving displays with a 33 MHz > > pixel clock (33 being a natural divider of 297). > > > > Running the DE clock at 297 MHz will typically result in parenting to > > the video pll instead of the periph0 pll, thus making the display > > output functional. > > > > This is all a bit fragile but it solves the issue with displays running > > at 33 Mhz and brings V3s to use the same frequency as other platforms, > > making support more unified. > > It's beyond fragile, and doesn't have anything to do with the DRM driver. > > You should set up the clock tree properly in the clock driver, and then > add NO_REPARENT to the DE clock to make sure it stays that way.
Thanks for the suggestion! I wasn't aware there was a flag to avoid reparenting, sounds like the most reasonable way to solve this issue then. I'll send another iteration reworking the clock tree then. > And then, you can change the clock rate if you want to, but at least you > don't set a rate and hope that the side effects work your way, and won't > happen again. We might as well still change it. To be honest I don't really see why it was set to 150 MHz in the first place. Cheers, Paul -- Paul Kocialkowski, Independent contractor - sys-base - https://www.sys-base.io/ Free software developer - https://www.paulk.fr/ Expert in multimedia, graphics and embedded hardware support with Linux.
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