linux-kernel - RE: [PATCH 1/2] dt-bindings: PCI: designware: Add binding for ZRX-DC PHY property

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Date:   Mon, 21 Oct 2019 20:26:28 +0530
From:   "Pankaj Dubey" <pankaj.dubey@...sung.com>
To:     "'Andrew Murray'" <andrew.murray@....com>,
        "'Anvesh Salveru'" <anvesh.s@...sung.com>
Cc:     <linux-pci@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <bhelgaas@...gle.com>,
        <gustavo.pimentel@...opsys.com>, <jingoohan1@...il.com>,
        <robh+dt@...nel.org>, <mark.rutland@....com>
Subject: RE: [PATCH 1/2] dt-bindings: PCI: designware: Add binding for
 ZRX-DC PHY property



> -----Original Message-----
> From: Andrew Murray <andrew.murray@....com>
> Sent: Monday, October 21, 2019 7:46 PM
> To: Anvesh Salveru <anvesh.s@...sung.com>
> Cc: linux-pci@...r.kernel.org; devicetree@...r.kernel.org; linux-
> kernel@...r.kernel.org; bhelgaas@...gle.com;
> gustavo.pimentel@...opsys.com; jingoohan1@...il.com; robh+dt@...nel.org;
> mark.rutland@....com; Pankaj Dubey <pankaj.dubey@...sung.com>
> Subject: Re: [PATCH 1/2] dt-bindings: PCI: designware: Add binding for
ZRX-DC
> PHY property
> 
> On Mon, Oct 21, 2019 at 05:55:55PM +0530, Anvesh Salveru wrote:
> > Add support for ZRX-DC compliant PHYs. If PHY is not compliant to
> > ZRX-DC specification, then after every 100ms link should transition to
> > recovery state during the low power states which increases power
> consumption.
> >
> > Platforms with ZRX-DC compliant PHY can use "snps,phy-zrxdc-compliant"
> > property in DesignWare controller DT node.
> >
> > Signed-off-by: Anvesh Salveru <anvesh.s@...sung.com>
> > Signed-off-by: Pankaj Dubey <pankaj.dubey@...sung.com>
> > ---
> >  Documentation/devicetree/bindings/pci/designware-pcie.txt | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/pci/designware-pcie.txt
> > b/Documentation/devicetree/bindings/pci/designware-pcie.txt
> > index 78494c4050f7..9507ac38ac89 100644
> > --- a/Documentation/devicetree/bindings/pci/designware-pcie.txt
> > +++ b/Documentation/devicetree/bindings/pci/designware-pcie.txt
> > @@ -38,6 +38,8 @@ Optional properties:
> >     for data corruption. CDM registers include standard PCIe
configuration
> >     space registers, Port Logic registers, DMA and iATU (internal
Address
> >     Translation Unit) registers.
> > +- snps,phy-zrxdc-compliant: This property is needed if phy complies
> > +with the
> 
> Strictly speaking, this is a property of the phy - not the controller that
uses it.
> 
> If I understand correctly, there are some DW based PCI controllers that
use a
> phandle reference in DT to a Phy (such as fsl,imx6q-pcie.txt). Therefore
it feels
> like this is in the wrong place. Is there a reason this isn't described in
the Phy?
>

Yes, from HW point of view this is a property of the PHY. As PHY is the one
which is ZRXDC compliant or non-compliant. 
But as the DW controller programming needs to be altered for handling such
phys, so we added it as a DT binding of DW controller driver. 
Also it might be possible that, some other PCIe controller (other than
DesignWare), do not have any such provision in controller H/W and they
expect PHY itself should expose some SFR to handle such scenario. In such
cases it is straight-forward to add this binding as part of PHY node.

We can add this as part of PHY binding, but in that case we will end up
checking PHY binding in DWC driver via PHY nodes which seems little a bit of
hack. 

Do you have any other better approach to handle this? 
 
> Thanks,
> 
> Andrew Murray
> 
> > +  ZRX-DC specification.
> >  RC mode:
> >  - num-viewport: number of view ports configured in hardware. If a
platform
> >    does not specify it, the driver assumes 2.
> > --
> > 2.17.1
> >