linux-kernel - Re: [PATCH 1/2] staging: r8188eu: Use usb_control_msg_recv/send() in usbctrl

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Date:   Tue, 24 Aug 2021 12:38:20 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Phillip Potter <phil@...lpotter.co.uk>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     Larry Finger <Larry.Finger@...inger.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:STAGING SUBSYSTEM" <linux-staging@...ts.linux.dev>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Pavel Skripkin <paskripkin@...il.com>
Subject: Re: [PATCH 1/2] staging: r8188eu: Use usb_control_msg_recv/send() in usbctrl_vendorreq()

On Tuesday, August 24, 2021 7:44:40 AM CEST Christophe JAILLET wrote:
> Le 24/08/2021 à 04:01, Fabio M. De Francesco a écrit :
> > On Tuesday, August 24, 2021 3:38:03 AM CEST Fabio M. De Francesco wrote:
> >> I think that I've inadvertently switched the order by which usb_control_msg_send()
> >> and memcpy() are called. I'm very sorry for not doing my tests, but (as I had said
> >> before) at the moment I don't have my device with me.
> > 
> > No, I did not switch them. There must be something else...
> > Sorry for the noise.
> > 
> > Fabio
> > 
> 
> Hi,
> 
> 'usb_control_msg_recv()' looks like:
> 
> int usb_control_msg_recv(struct usb_device *dev, __u8 endpoint, ...)
> {
> 	unsigned int pipe = usb_rcvctrlpipe(dev, endpoint);
> 	...
> 	ret = usb_control_msg(dev, pipe, ...);
> 
> 
> 'usb_control_msg()' looks like:
> int usb_control_msg(struct usb_device *dev, unsigned int pipe, ...)
> {
> 
> The difference is that one expect an 'endpoint' (and compute the pipe 
> from it), and the other expect a 'pipe'.

Hi Christophe,

Yes, correct. That's why I changed the type of 'pipe' from "unsigned int"
to "u8". I also saw that usb_control_msg_recv/send take care of calling 
usb_rcvctrpipe() and usb_sndctrlpipe(); so, in my patch I deleted 
those calls.

Not related to my patch... why Linux has u8 and __u8? What are the  
different use cases they are meant for? 

> Also, in your code, 'pipe' looks un-initialized.

Oh yes, good catch.  Thanks!

> So, my guess is that you should rename 'pipe' into 'endpoint' (to keep 
> the semantic),
> have "endpoint = 0;" somewhere and pass it to 
> usb_control_msg_{recv|send}.
> Or just remove 'pipe' and pass an explicit 0 directly.

I've just seen that in other drivers the code passes an explicit 0.
So, also according to your suggestion, I'll remove "pipe/endpoint".

> Not sure it is enough, but it looks like a difference between before and 
> after your patch.

Since I cannot see other issues, I'm about to fix the code as said above and
then submit a v2 series.

Your 2c are worth much more than how much you think :)

Thanks very much,

Fabio

> just my 2c,
> CJ
>