linux-kernel - Re: [PATCH v3 1/3] Documentation: dt-bindings: Add snps,need-phy-for-wake for dwc2 USB

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Date:   Thu, 13 Jun 2019 17:06:07 -0600
From:   Rob Herring <robh@...nel.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Minas Harutyunyan <hminas@...opsys.com>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>, heiko@...ech.de,
        Alan Stern <stern@...land.harvard.edu>,
        Artur Petrosyan <Arthur.Petrosyan@...opsys.com>,
        amstan@...omium.org, linux-rockchip@...ts.infradead.org,
        William Wu <william.wu@...k-chips.com>,
        linux-usb@...r.kernel.org, Stefan Wahren <stefan.wahren@...e.com>,
        Randy Li <ayaka@...lik.info>, zyw@...k-chips.com,
        mka@...omium.org, ryandcase@...omium.org,
        Amelie Delaunay <amelie.delaunay@...com>, jwerner@...omium.org,
        Elaine Zhang <zhangqing@...k-chips.com>,
        Douglas Anderson <dianders@...omium.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v3 1/3] Documentation: dt-bindings: Add
 snps,need-phy-for-wake for dwc2 USB

On Mon, 20 May 2019 10:56:03 -0700, Douglas Anderson wrote:
> Some SoCs with a dwc2 USB controller may need to keep the PHY on to
> support remote wakeup.  Allow specifying this as a device tree
> property.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> For relevant prior discussion on this patch, see:
> 
> https://lkml.kernel.org/r/1435017144-2971-3-git-send-email-dianders@chromium.org
> 
> I didn't make any changes from the prior version since I never found
> out what Rob thought of my previous arguments.  If folks want a
> change, perhaps they could choose from these options:
> 
> 1. Assume that all dwc2 hosts would like to keep their PHY on for
>    suspend if there's a USB wakeup enabled, thus we totally drop this
>    binding.  This doesn't seem super great to me since I'd bet that
>    many devices that use dwc2 weren't designed for USB wakeup (they
>    may not keep enough clocks or rails on) so we might be wasting
>    power for nothing.
> 2. Rename this property to "snps,wakeup-from-suspend-with-phy" to make
>    it more obvious that this property is intended both to document
>    that wakeup from suspend is possible and that we need the PHY for
>    said wakeup.
> 3. Rename this property to "snps,can-wakeup-from-suspend" and assume
>    it's implicit that if we can wakeup from suspend that we need to
>    keep the PHY on.  If/when someone shows that a device exists using
>    dwc2 where we can wakeup from suspend without the PHY they can add
>    a new property.
> 
> NOTE FOR REPOST:
> - In v2 Rob said [1] he'd prefer something based on the SoC
>   compatibility string, but that doesn't work because not all boards
>   will have the regulator setup / board design / suspend logic
>   necessary to make this work.
> 
> [1] https://lkml.kernel.org/r/20190430012328.GA25660@bogus
> 
> 
> Changes in v3: None
> Changes in v2: None
> 
>  Documentation/devicetree/bindings/usb/dwc2.txt | 3 +++
>  1 file changed, 3 insertions(+)
> 

Reviewed-by: Rob Herring <robh@...nel.org>