linux-kernel - Re: [PATCH V13 08/12] dt-bindings: Add PCIe supports-clkreq property

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Message-ID: <20190710152856.GB8781@e121166-lin.cambridge.arm.com>
Date:   Wed, 10 Jul 2019 16:28:56 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Vidya Sagar <vidyas@...dia.com>
Cc:     bhelgaas@...gle.com, robh+dt@...nel.org, mark.rutland@....com,
        thierry.reding@...il.com, jonathanh@...dia.com, kishon@...com,
        catalin.marinas@....com, will.deacon@....com, jingoohan1@...il.com,
        gustavo.pimentel@...opsys.com, digetx@...il.com,
        mperttunen@...dia.com, linux-pci@...r.kernel.org,
        devicetree@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kthota@...dia.com, mmaddireddy@...dia.com, sagar.tv@...il.com
Subject: Re: [PATCH V13 08/12] dt-bindings: Add PCIe supports-clkreq property

On Wed, Jul 10, 2019 at 11:52:08AM +0530, Vidya Sagar wrote:
> Some host controllers need to know the existence of clkreq signal routing to
> downstream devices to be able to advertise low power features like ASPM L1
> substates. Without clkreq signal routing being present, enabling ASPM L1 sub
> states might lead to downstream devices falling off the bus. Hence a new device

You mean "being disconnected from the bus" right ? I will update it.

Lorenzo

> tree property 'supports-clkreq' is added to make such host controllers
> aware of clkreq signal routing to downstream devices.
> 
> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
> Reviewed-by: Rob Herring <robh@...nel.org>
> Reviewed-by: Thierry Reding <treding@...dia.com>
> ---
> V13:
> * None
> 
> V12:
> * Rebased on top of linux-next top of the tree
> 
> V11:
> * None
> 
> V10:
> * None
> 
> V9:
> * None
> 
> V8:
> * None
> 
> V7:
> * None
> 
> V6:
> * s/Documentation\/devicetree/dt-bindings/ in the subject
> 
> V5:
> * None
> 
> V4:
> * Rebased on top of linux-next top of the tree
> 
> V3:
> * None
> 
> V2:
> * This is a new patch in v2 series
> 
>  Documentation/devicetree/bindings/pci/pci.txt | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/pci/pci.txt b/Documentation/devicetree/bindings/pci/pci.txt
> index 2a5d91024059..29bcbd88f457 100644
> --- a/Documentation/devicetree/bindings/pci/pci.txt
> +++ b/Documentation/devicetree/bindings/pci/pci.txt
> @@ -27,6 +27,11 @@ driver implementation may support the following properties:
>  - reset-gpios:
>     If present this property specifies PERST# GPIO. Host drivers can parse the
>     GPIO and apply fundamental reset to endpoints.
> +- supports-clkreq:
> +   If present this property specifies that CLKREQ signal routing exists from
> +   root port to downstream device and host bridge drivers can do programming
> +   which depends on CLKREQ signal existence. For example, programming root port
> +   not to advertise ASPM L1 Sub-States support if there is no CLKREQ signal.
>  
>  PCI-PCI Bridge properties
>  -------------------------
> -- 
> 2.17.1
>