Re: [Freedreno] [v1] drm/msm/dsi/pll: call vco set rate explicitly

Jeffrey Hugo
2020-02-07T14:11:08Z

On Fri, Feb 7, 2020 at 5:38 AM <harigovi@codeaurora.org> wrote:
>
> On 2020-02-06 20:29, Jeffrey Hugo wrote:
> > On Thu, Feb 6, 2020 at 2:13 AM Harigovindan P <harigovi@codeaurora.org>
> > wrote:
> >>
> >> For a given byte clock, if VCO recalc value is exactly same as
> >> vco set rate value, vco_set_rate does not get called assuming
> >> VCO is already set to required value. But Due to GDSC toggle,
> >> VCO values are erased in the HW. To make sure VCO is programmed
> >> correctly, we forcefully call set_rate from vco_prepare.
> >
> > Is this specific to certain SoCs? I don't think I've observed this.
>
> As far as Qualcomm SOCs are concerned, since pll is analog and the value
> is directly read from hardware if we get recalc value same as set rate
> value, the vco_set_rate will not be invoked. We checked in our idp
> device which has the same SOC but it works there since the rates are
> different.

This doesn't seem to be an answer to my question. What Qualcomm SoCs
does this issue apply to? Everything implementing the 10nm pll? One
specific SoC? I don't believe I've seen this on MSM8998, nor SDM845,
so I'm interested to know what is the actual impact here. I don't see
an "IDP" SoC in the IP catalog, so I really have no idea what you are
referring to.