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Date:   Sun, 6 Nov 2022 15:22:19 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Vincent MAILHOL <mailhol.vincent@wanadoo.fr>
Cc:     Alan Stern <stern@rowland.harvard.edu>, linux-can@vger.kernel.org,
        Marc Kleine-Budde <mkl@pengutronix.de>,
        linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org
Subject: Re: [PATCH v2 3/3] can: etas_es58x: report the firmware version
 through ethtool
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On Sun, Nov 06, 2022 at 09:47:05PM +0900, Vincent MAILHOL wrote:
> On Sun. 6 Nov. 2022 at 20:25, Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
> > On Sat, Nov 05, 2022 at 08:45:10PM -0400, Alan Stern wrote:
> > > On Sat, Nov 05, 2022 at 06:38:35PM +0100, Greg Kroah-Hartman wrote:
> > > > On Sun, Nov 06, 2022 at 02:21:11AM +0900, Vincent MAILHOL wrote:
> > > > > On Sat. 5 Nov. 2022 at 18:27, Vincent MAILHOL
> > > > > <mailhol.vincent@wanadoo.fr> wrote:
> > > > > > On Sat. 5 Nov. 2022 at 17:36, Greg Kroah-Hartman
> > > > > > <gregkh@linuxfoundation.org> wrote:
> > > > It's late right now, and I can't remember the whole USB spec, but I
> > > > think the device provides a list of the string ids that are valid for
> > > > it.  If so, we can add that to sysfs for any USB device out there, no
> > > > matter the string descriptor number.
> > >
> > > No, there is no such list.
> >
> > Yeah, my fault, nevermind about that, sorry.
> >
> > > > If not, maybe we can just iterate the 255 values and populate sysfs
> > > > files if they are present?  I'll dig up the USB spec tomorrow...
> > >
> > > Yes, we could do that.  But the filename would have to be the string
> > > id, which is not meaningful.  We wouldn't be able to have labels like
> > > "product-info" unless somehow a driver could provide the label.
> >
> > We could have a directory of strings/ with the individual descriptors in
> > there as files with the name being the string id.
> >
> > But that might take a long time to populate, as it can take a few tries
> > to get the string from a device, and to do that 256 times might be
> > noticable at device insertion time.
> >
> > > Also, there's the matter of language.  Devices can have string
> > > descriptors in multiple languages; which one should we show in sysfs?
> > > All of them?  Right now we use just the default language for the strings
> > > that we put in sysfs.
> > >
> > > > I say do this at the USB core level, that way it works for any USB
> > > > device, and you don't have a device-specific sysfs file and custom
> > > > userspace code just for this.
> > >
> > > This is unavoidable to some extent.  Without device-specific information
> > > or userspace code, there is no way to know which string descriptor
> > > contains the data you want.
> >
> > Agreed.
> >
> > Ok, for this specific instance, adding the "we know this string id
> > should be here" as a device-specific sysfs file seems to be the easiest
> > way forward.
> >
> > Vincent, want to try that instead?
> 
> OK for me. Will do that and remove the kernel log spam and replace it
> by a sysfs entry.
> 
> I have two questions:
> 
> 1/ Can I still export and use usb_cache_string()? In other terms, does
> the first patch of this series still apply? This looks like the most
> convenient function to retrieve that custom string to me.

Everyone seems to just use the usb_string() function, will that not work
for you?

> 2/ Is it a no-go to also populate ethtool_drvinfo::fw_version? Some
> users might look for the value in sysfs, while some might use ethtool.
> If the info is not available in ethtool, people might simply assume it
> is not available at all. So, I would like to provide both.

That's up to the network developers/maintainers.  I don't know if that's
a required or common api for network devices to have.

thanks,

greg k-h