netdev - Re: [PATCH net-next 05/10] lan78xx: Disable USB3 link power state transitions

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Message-ID: <20210824081958.407b4009@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 24 Aug 2021 08:19:58 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     "John Efstathiades" <john.efstathiades@...blebay.com>
Cc:     <linux-usb@...r.kernel.org>, <UNGLinuxDriver@...rochip.com>,
        <woojung.huh@...rochip.com>, <davem@...emloft.net>,
        <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 05/10] lan78xx: Disable USB3 link power state
 transitions

On Tue, 24 Aug 2021 15:33:13 +0100 John Efstathiades wrote:
> > Do you expect the device-initiated transitions to always be causing
> > trouble or are there scenarios where they are useful?  
> 
> It's a particular problem on Android devices.
> 
> > Having to recompile the driver is a middle ground rarely chosen
> > upstream. If the code has very low chance of being useful - let's
> > remove it (git will hold it forever if needed); if there are reasonable
> > chances someone will find it useful it should be configurable from user
> > space, or preferably automatically enabled based on some device match
> > list.  
> 
> I like the sound of the device match list but I don't know what you mean.
> Is there a driver or other reference you could point me at that provides
> additional info?

Depends on what the discriminator is. If problems happen with 
a particular ASIC revisions driver needs to read the revision
out and make a match. If it's product by product you can use
struct usb_device_id :: driver_info to attach metadata per 
device ID. If it's related to the platform things like DMI
matching are sometimes used. I have very limited experience 
with Android / embedded ARM so not sure what would work there.