linux-kernel - Re: [PATCH] net: usb: ax88179_178a: avoid failed operations when device is disconnected

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Message-ID: <20231130172525.193069-1-jtornosm@redhat.com>
Date:   Thu, 30 Nov 2023 18:25:21 +0100
From:   Jose Ignacio Tornos Martinez <jtornosm@...hat.com>
To:     stern@...land.harvard.edu
Cc:     davem@...emloft.net, edumazet@...gle.com, jtornosm@...hat.com,
        kuba@...nel.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, netdev@...r.kernel.org,
        oneukum@...e.com, pabeni@...hat.com
Subject: Re: [PATCH] net: usb: ax88179_178a: avoid failed operations when device is disconnected

Hi Alan,

Thank you again for you comments.

> What are these unnecessary operations?
Sorry if I was not clear, I was referring to the reading and writing 
operations that are commanded within stop and unbind driver functions.
This operations are necessary if we unbind to get the device stopped in
a known state but if the device is detached, they are failing and imho
they are not necessary. That is the reason why I was trying to detect 
when the device is really disconnected, to allow sending commands only
if the device was still connected. 

> In general, drivers should treat "unbind" the same as "disconnect" (in
> both cases, the ->disconnect() routine is called).  If a driver tries to
> send commands to the device while the disconnect routine is running, it
> should expect that they might fail and not generate an error message if
> they do.
>
> (Also, note that the USB core will allow a driver to send commands to
> the device during unbind only if the .soft_unbind flag is set in the
> usb_driver structure.)
>
> And in any case, a driver should _never_ try to communicate with the
> device after the disconnect routine has returned.
Ok, understood, very helpful clarification.
In any case, I was referring to the internal operations during stop and
unbind. And if any failed operations are commanded before and after
disconnection (if any), try to detect with the warning to be sure if there
is any problem.

I have checked that other drivers are using USB_STATE_NOTATTACHED to check
and confirm the device disconnection. And I am trying to analyze other 
drivers to check if this can be done in another way. 
If I use -ENODEV as Oliver suggested, I think I wouldn't know if the device
is disconnected previous to any operation. But maybe this is the way.

Best regards
José Ignacio