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

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Date:   Fri, 24 Jun 2022 08:46:30 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Neal Liu <neal_liu@...eedtech.com>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        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-kernel@...r.kernel.org, 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

What is "TOC"?  What is "format 1"?

> Windows OS.

Which versions of Windows support this?

> This patch is tested on Windows OS Server 2019.

Does this fix a regression where we used to support this?  Or is this a
new feature of Windows?


> 
> 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 */
>  		len = 4 + 2*8;		/* 4 byte header + 2 descriptors */
>  		memset(buf, 0, len);
>  		buf[1] = len - 2;	/* TOC Length excludes length field */
> @@ -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 */

So case 1 is "multi-session"?  Please document this properly.

thanks,

greg k-h