FYI: i.MX8MP ISP (RKISP1) MI registers corruption: resolved

[Krzysztof Hałasa]

Hi,

summary:

I've done a few additional tests and it seems the MEDIA_AXI clock is the
problem. Reducing it to 400 MHz while still running MEDIA_ISP at 500 MHz
produces no errors.
MEDIA_ISP at 400 MHz and MEDIA_AXI at 500 MHz produces errors, though
(register address errors while reading and writing from/to ISP MI
(memory interface) registers, only on the secondary ISP (isp1), and
generally only while streaming data from the ISP).

What is driven by MEDIA_AXI clock root? MEDIAMIX: ISI, LCDIF, ISP, DWE.

According to both datasheets (industrial and commercial), MEDIA_AXI
is limited to 400 MHz in normal mode and 500 MHz in overdrive mode.
All my hardware is setup for overdrive mode, though (two manufacturers,
both using the same PMIC setup).

Since no hardware in the official Linux kernel tree (DT) uses the second
ISP... Should we just add a warning to the imx8mp.dtsi and be done with
it?
Out of tree hardware using isp1 (csi1) obviously exists.
-- 
Krzysztof "Chris" Hałasa

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