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Date:   Sun, 6 Nov 2022 12:21:39 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Alan Stern <stern@rowland.harvard.edu>
Cc:     Vincent MAILHOL <mailhol.vincent@wanadoo.fr>,
        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 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?

thanks,

greg k-h