Re: [PATCH 08/13] phy: qcom-qmp-pcie: drop power-down delay config

[Dmitry Baryshkov]

On 11/10/2022 16:53, Johan Hovold wrote:
> On Tue, Oct 11, 2022 at 04:46:53PM +0300, Dmitry Baryshkov wrote:
> > On 11/10/2022 16:14, Johan Hovold wrote:
> > > The power-down delay was included in the first version of the QMP driver
> > > as an optional delay after powering on the PHY (using
> > > POWER_DOWN_CONTROL) and just before starting it. Later changes modified
> > > this sequence by powering on before initialising the PHY, but the
> > > optional delay stayed where it was (i.e. before starting the PHY).
> > >
> > > The vendor driver does not use a delay before starting the PHY and this
> > > is likely not needed on any platform unless there is a corresponding
> > > delay in the vendor kernel init sequence tables (i.e. in devicetree).
> > >
> > > Let's keep the delay for now, but drop the redundant delay period
> > > configuration while increasing the unnecessarily low timer slack
> > > somewhat.
> >
> > Actually, the vendor driver does this 995..1005 sleep. But contrary to
> > our driver it does that after programming whole PHY init sequence, which
> > includes SW_RESET / START_CTL, but before programming the pipe clocks.
>
> Right, it does it after starting the PHY which means that you don't have
> to poll for as long for the PHY status.
>
> It's a different delay entirely.

No-no-no. The 995-1005 delay was added guess for which SoC? For ipq8074, 
where the config tables contain the ugly CFG_L writes for SW_RESET / 
START_CTRL. So, it is the same delay, but added by somebody who didn't 
care enough. The original 10-11 delay is a completely different story, 
you are correct here.

Thus, I'd say, the PCIe delay should be moved after the registers 
programming.

> > I think we can either drop this delay completely, or move it before
> > read_poll_timeout().
>
> It definitely shouldn't be used for any new platforms, but I opted for
> the conservative route of keeping it in case some of the older platforms
> actually do need it.
>
> My bet is that this is all copy-paste cruft that could be removed, but
> I'd rather do that as a separate follow-on change. Perhaps after testing
> some more SoC after removing the delay.
>
> SC8280XP certainly doesn't need it.

I think in our case this delay just falls into status polling. We'd 
probably need it, if we'd add the noretain handling.

> Johan

--
With best wishes
Dmitry