linux-kernel - Re: [PATCH v12 2/6] PCI: mediatek: Add new method to get shared pcie-cfg base address

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Message-ID: <eb855d186d572e8a0343456bb5d76797f8f3870f.camel@mediatek.com>
Date:   Thu, 2 Sep 2021 17:34:08 +0800
From:   Chuanjia Liu <chuanjia.liu@...iatek.com>
To:     Rob Herring <robh+dt@...nel.org>
CC:     Bjorn Helgaas <helgaas@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Ryder Lee <ryder.lee@...iatek.com>,
        "Jianjun Wang" <jianjun.wang@...iatek.com>,
        Yong Wu <yong.wu@...iatek.com>,
        PCI <linux-pci@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>, <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v12 2/6] PCI: mediatek: Add new method to get shared
 pcie-cfg base address

On Tue, 2021-08-31 at 10:17 -0500, Rob Herring wrote:
> On Mon, Aug 30, 2021 at 10:31 PM Chuanjia Liu <
> chuanjia.liu@...iatek.com> wrote:
> > 
> > On Mon, 2021-08-30 at 16:43 -0500, Bjorn Helgaas wrote:
> > > On Mon, Aug 30, 2021 at 03:09:44PM +0800, Chuanjia Liu wrote:
> > > > On Fri, 2021-08-27 at 11:46 -0500, Bjorn Helgaas wrote:
> > > > > On Mon, Aug 23, 2021 at 11:27:56AM +0800, Chuanjia Liu wrote:
> > > > > > @@ -995,6 +1004,14 @@ static int
> > > > > > mtk_pcie_subsys_powerup(struct
> > > > > > mtk_pcie *pcie)
> > > > > >                         return PTR_ERR(pcie->base);
> > > > > >         }
> > > > > > 
> > > > > > +       cfg_node = of_find_compatible_node(NULL, NULL,
> > > > > > +                                          "mediatek,generi
> > > > > > c-
> > > > > > pciecfg");
> > > > > > +       if (cfg_node) {
> > > > > > +               pcie->cfg =
> > > > > > syscon_node_to_regmap(cfg_node);
> > > > > 
> > > > > Other drivers in drivers/pci/controller/ use
> > > > > syscon_regmap_lookup_by_phandle() (j721e, dra7xx, keystone,
> > > > > layerscape, artpec6) or syscon_regmap_lookup_by_compatible()
> > > > > (imx6,
> > > > > kirin, v3-semi).
> > > > > 
> > > > > You should do it the same way unless there's a need to be
> > > > > different.
> > > > 
> > > > I have used phandle, but Rob suggested to search for the node
> > > > by
> > > > compatible.
> > > > The reason why syscon_regmap_lookup_by_compatible() is not
> > > > used here is that the pciecfg node is optional, and there is no
> > > > need to
> > > > return error when the node is not searched.
> > > 
> > > How about this?
> > > 
> > >   regmap = syscon_regmap_lookup_by_compatible("mediatek,generic-
> > > pciecfg");
> > >   if (!IS_ERR(regmap))
> > >     pcie->cfg = regmap;
> 
> +1
> 
> > 
> > Hi Bjorn,
> > 
> > We need to deal with three situations
> > 1) No error
> > 2) The error of the node not found, don't do anything
> > 3) Other errors, return errors
> > 
> > I guess you mean
> > 
> > regmap = syscon_regmap_lookup_by_compatible("mediatek,generic-
> > pciecfg");
> >   if (!IS_ERR(regmap))
> >       pcie->cfg = regmap;
> >   else if (IS_ERR(regmap) && PTR_ERR(regmap) != -ENODEV)
> 
> You already know  IS_ERR is true here.
> 
> >       return PTR_ERR(regmap);
> 
> syscon_regmap_lookup_by_compatible_optional is the function you are
> looking for. The _optional flavor doesn't exist, so create it. There
> is one for the phandle lookup.
> 
> > 
> > I'm not sure if we need this, it seems a little weird and there are
> > many drivers in other subsystems that use syscon_node_to_regmap().
> 
> You are implementing the exact same sequence that
> syscon_regmap_lookup_by_compatible() does, so clearly you should be
> using it. The one difference is you forgot the of_node_put().

Hi,Rob
Thanks for your explanation. You're right. 
Now I understand use syscon_regmap_lookup_by_compatible() is a better
way. I'll follow your advice

regmap = syscon_regmap_lookup_by_compatible("mediatek,generic-
pciecfg");
if (!IS_ERR(regmap))
	pcie->cfg = regmap;
else if (PTR_ERR(regmap) != -ENODEV)
	return PTR_ERR(regmap);

Best regards
Chuanjia

> 
> Rob
> 
> _______________________________________________
> Linux-mediatek mailing list
> Linux-mediatek@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-mediatek

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