Re: [PATCH] drm/omap: Migrate minimum FCK/PCK ratio from Kconfig to dts

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On 30/09/2019 17:12, Adam Ford wrote:

I don't know the implications, so if the people from TI say stick with
16, I'm fine with that, but at least there is some evidence that it
can be higher than 16, but lower than 32.


Sorry for all the spam, but I moved both of them to 31 from 32, and it
also seems to work successfully at 31.

[   26.923004] DSS: set fck to 36000000
[   26.923034] DISPC: lck = 36000000 (1)
[   26.923034] DISPC: pck = 9000000 (4)
[   26.925048] DISPC: channel 0 xres 480 yres 272
[   26.925048] DISPC: pck 9000000
[   26.925048] DISPC: hsync_len 42 hfp 3 hbp 2 vsw 11 vfp 2 vbp 3
[   26.925079] DISPC: vsync_level 1 hsync_level 1 data_pclk_edge 1
de_level 1 sync_pclk_edge -1
[   26.925079] DISPC: hsync 17077Hz, vsync 59Hz
[   27.384613] DISPC: dispc_runtime_put

Is it possible to use 31?

Let's see what Tero says, but yeah, something is odd here. I expected the max divider to be 16 with Tero's patch, but I don't see it having that effect. I can get the div to 31.

You can see this from the clock register 0x48004e40 (CM_CLKSEL_DSS). The lowest bits are the divider, 5 to 0. The TRM says max div is 32.

Tero said for him the dividers > 16 didn't "stick" to the register. I'm now wondering if he has an old beagleboard with OMAP34xx, which has max div 16.

 Tomi

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