linux-kernel - Re: [PATCH v14 05/11] PCI: kirin: give more time for PERST# reset to finish

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Date:   Thu, 21 Oct 2021 13:40:18 +0100
From:   Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     linuxarm@...wei.com, mauro.chehab@...wei.com,
        Krzysztof Wilczyński 
        <kw@...ux.com>, Songxiaowei <songxiaowei@...ilicon.com>,
        Binghui Wang <wangbinghui@...ilicon.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh@...nel.org>, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH v14 05/11] PCI: kirin: give more time for PERST# reset
 to finish

Em Thu, 21 Oct 2021 13:27:29 +0100
Lorenzo Pieralisi <lorenzo.pieralisi@....com> escreveu:

> On Tue, Oct 19, 2021 at 07:06:42AM +0100, Mauro Carvalho Chehab wrote:
> > Before code refactor, the PERST# signals were sent at the
> > end of the power_on logic. Then, the PCI core would probe for
> > the buses and add them.
> > 
> > The new logic changed it to send PERST# signals during
> > add_bus operation. That altered the timings.
> > 
> > Also, HiKey 970 require a little more waiting time for
> > the PCI bridge - which is outside the SoC - to finish
> > the PERST# reset, and then initialize the eye diagram.
> >   
> 
> Ok, now you explained it and we should move this explanation
> in the commit log that this change is affecting (I mean we
> should squash this patch with the patch that actually requires it
> - I am not sure whether it is patch 6 or another one).

IMO, having it on a separate patch has the advantage of better documenting
this single line change, but yeah, this is part of the change needed to
handle PERST# on a more portable way to work for both chipsets.

> I can do it for you; I thought it would be a standalone change
> but it actually isn't, because it is brought about by the
> changes you are making and therefore there it belongs.

Feel free to squash this patch if you prefer so. whatever works best for you.

> Thanks for explaining it and apologies for the churn.

No problem.
 
> 
> Lorenzo
> 
> > So, increase the waiting time for the PERST# signals to
> > what's required for it to also work with HiKey 970.
> > 
> > Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
> > ---
> > 
> > See [PATCH v14 00/11] at: https://lore.kernel.org/all/cover.1634622716.git.mchehab+huawei@kernel.org/
> > 
> >  drivers/pci/controller/dwc/pcie-kirin.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-kirin.c b/drivers/pci/controller/dwc/pcie-kirin.c
> > index de375795a3b8..bc329673632a 100644
> > --- a/drivers/pci/controller/dwc/pcie-kirin.c
> > +++ b/drivers/pci/controller/dwc/pcie-kirin.c
> > @@ -113,7 +113,7 @@ struct kirin_pcie {
> >  #define CRGCTRL_PCIE_ASSERT_BIT		0x8c000000
> >  
> >  /* Time for delay */
> > -#define REF_2_PERST_MIN		20000
> > +#define REF_2_PERST_MIN		21000
> >  #define REF_2_PERST_MAX		25000
> >  #define PERST_2_ACCESS_MIN	10000
> >  #define PERST_2_ACCESS_MAX	12000
> > -- 
> > 2.31.1
> >