linux-kernel - RE: [PATCH v2] usb: gadget: f_mass_storage: Make CD-ROM emulation works with Windows OS

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Date:   Mon, 27 Jun 2022 02:56:40 +0000
From:   Neal Liu <neal_liu@...eedtech.com>
To:     Alan Stern <stern@...land.harvard.edu>
CC:     Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Roger Quadros <roger.quadros@...ia.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Wesley Cheng <quic_wcheng@...cinc.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Matthew Wilcox <willy@...radead.org>,
        Nikita Yushchenko <nikita.yoush@...entembedded.com>,
        Cai Huoqing <cai.huoqing@...ux.dev>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        BMC-SW <BMC-SW@...eedtech.com>
Subject: RE: [PATCH v2] usb: gadget: f_mass_storage: Make CD-ROM emulation
 works with Windows OS

> On Fri, Jun 24, 2022 at 10:19:16AM +0800, Neal Liu wrote:
> > Add read TOC with format 1 to support CD-ROM emulation with Windows
> > OS.
> > This patch is tested on Windows OS Server 2019.
> >
> > Signed-off-by: Neal Liu <neal_liu@...eedtech.com>
> > ---
> >  drivers/usb/gadget/function/f_mass_storage.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/usb/gadget/function/f_mass_storage.c
> > b/drivers/usb/gadget/function/f_mass_storage.c
> > index 3a77bca0ebe1..9edf76c22605 100644
> > --- a/drivers/usb/gadget/function/f_mass_storage.c
> > +++ b/drivers/usb/gadget/function/f_mass_storage.c
> > @@ -1209,7 +1209,8 @@ static int do_read_toc(struct fsg_common
> > *common, struct fsg_buffhd *bh)
> >
> >  	switch (format) {
> >  	case 0:
> > -		/* Formatted TOC */
> > +	case 1:
> > +		/* Formatted TOC, Session info */
> 
> This comment is a little misleading.  0 is formatted TOC, and 1 is
> multi-session info.  The way you wrote it, it looks like the comment applies to
> both formats.  Do it like this:
> 
> 	case 0:		/* Formatted TOC */
> 	case 1:		/* Multi-session info */
> 

Okay, looks more clear. I'll fix it in next patch.

> >  		len = 4 + 2*8;		/* 4 byte header + 2 descriptors */
> >  		memset(buf, 0, len);
> >  		buf[1] = len - 2;	/* TOC Length excludes length field */
> 
> It looks like you ignored one of the problems I pointed out in my earlier email:
> 
> > When format is 1, the driver is supposed to ignore the start_track
> > value.  Your patch does not do this.
> 
> Please fix this.
> 

Do you mean ignore the "start_track > 1" above?
Do this check only for format 0? Or format 0 & 2?

> 
> > @@ -1250,7 +1251,7 @@ static int do_read_toc(struct fsg_common
> *common, struct fsg_buffhd *bh)
> >  		return len;
> >
> >  	default:
> > -		/* Multi-session, PMA, ATIP, CD-TEXT not supported/required */
> > +		/* PMA, ATIP, CD-TEXT not supported/required */
> >  		curlun->sense_data = SS_INVALID_FIELD_IN_CDB;
> >  		return -EINVAL;
> >  	}
> > --
> > 2.25.1
> >