linux-kernel - Re: [PATCH V2 3/5] usb: xhci: tegra: Add genpd support

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Message-ID: <20181012102732.GD9162@ulmo>
Date:   Fri, 12 Oct 2018 12:27:32 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Jon Hunter <jonathanh@...dia.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-tegra@...r.kernel.org, Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH V2 3/5] usb: xhci: tegra: Add genpd support

On Fri, Oct 12, 2018 at 09:41:35AM +0100, Jon Hunter wrote:
> 
> On 11/10/18 17:47, Thierry Reding wrote:
> > On Fri, Sep 28, 2018 at 03:11:48PM +0100, Jon Hunter wrote:
> >> The generic power-domain framework has been updated to allow devices
> >> that require more than one power-domain to create a new device for
> >> each power-domain required and then link these new power-domain
> >> devices to the consumer device.
> >>
> >> Update the Tegra xHCI driver to use the new APIs provided by the
> >> generic power-domain framework so we can use the generic power-domain
> >> framework for managing the xHCI controllers power-domains. Please
> >> note that to maintain backward compatibility with older device-tree
> >> blobs these new generic power-domain APIs are only used if the
> >> 'power-domains' property is present and otherwise we fall back to
> >> using the legacy Tegra APIs for managing the power-domains.
> >>
> >> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
> >> ---
> >>  drivers/usb/host/xhci-tegra.c | 89 +++++++++++++++++++++++++++++++++++++------
> >>  1 file changed, 77 insertions(+), 12 deletions(-)
> > 
> > It'd be nice if we could eventually get rid of the legacy Tegra APIs,
> > but that's a separate issue, and this patch looks fine as-is:
> 
> Unfortunately, I don't think it is possible as it will break DT backward
> compatibility. However, one way to do it would be to force on all power
> domains on boot if PM is not supported.

Yeah, that sounds like a good option. If we don't support PM the I
imagine there's little use in keeping some of the partitions disabled.
But let's investigate that at a later time.

Thierry

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