According to the most up to date version of the dwc2 databook, the FRINT
field of the HFIR register should be programmed to:
* 125 us * (PHY clock freq for HS) - 1
* 1000 us * (PHY clock freq for FS/LS) - 1
This is opposed to older versions of the doc that claimed it should be:
* 125 us * (PHY clock freq for HS)
* 1000 us * (PHY clock freq for FS/LS)
In case you didn't spot it, the difference is the "- 1".
Let's add the "- 1" to match the newest user manual. It's presumed that
the "- 1" should have always been there and that this was always a
documentation error. If some hardware needs the "- 1" and other
hardware doesn't, we'll have to add a configuration parameter for it in
the future.
I checked things before and after this patch on rk3288 using a Total
Phase Beagle 5000 analyzer.
Before this patch, a low speed mouse shows constant Frame Timing Jitter
errors. After this patch errors have gone away.
Before this patch SOF packets move forward about 1 us per 4 ms. After
this patch the SOF packets move backward about 1 us per 255 ms. Some
specific SOF timestamps from the analyzer are below.
Acked-by: John Youn <johnyoun@synopsys.com> Signed-off-by: Douglas Anderson <dianders@chromium.org> Tested-by: Heiko Stuebner <heiko@sntech.de> Signed-off-by: Felipe Balbi <balbi@kernel.org>