linux-kernel - Re: [PATCH 1/3] usb: gadget: storage: Add fsg_get

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Date:	Thu, 10 Mar 2011 16:54:19 +0200
From:	Roger Quadros <roger.quadros@...ia.com>
To:	ext Alan Stern <stern@...land.harvard.edu>
CC:	<gregkh@...e.de>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] usb: gadget: storage: Add fsg_get_toc helper

Hi,

On 03/09/2011 06:07 PM, ext Alan Stern wrote:
>> +	case 2:
>> +		/* Raw TOC */
>> +		memset(buf, 0, 37);	/* Header + A0, A1&  A2 descriptors */
>> +		buf[1] = 37;		/* 4 + 3*11 */
>
> According to the SFF8020i spec Table 128, TOC Data Length is 2 + 11 *
> (number of descriptors returned).  But that's probably a misprint.

It's probably right. I will fix it and verify if it works.
>
>> +		buf[2] = 1;		/* First complete session */
>> +		buf[3] = 2;		/* Last complete session */
>
> According to the spec, for drives that do not support multi-session,
> the First session number should be equal to the Last session number.
>
Right. good catch.

>
> On Wed, 9 Mar 2011, Roger Quadros wrote:
>
>> Mac OS-X expects CD-ROM TOC in raw format (i.e. format:2). It also
>> sends the READ_TOC CDB in old style SFF8020i format. i.e. 2 format bits
>> are encoded in MSBs of CDB byte 9.
>>
>> This patch will enable CD-ROM emulation to work with Mac OS-X. Tested on
>> Mac OS X v10.6.3.
>>
>> Signed-off-by: Roger Quadros<roger.quadros@...ia.com>
>> ---
>>   drivers/usb/gadget/file_storage.c |   32 +++++++++++++++++++-------------
>>   1 files changed, 19 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/usb/gadget/file_storage.c b/drivers/usb/gadget/file_storage.c
>> index a6eacb5..753ac94 100644
>> --- a/drivers/usb/gadget/file_storage.c
>> +++ b/drivers/usb/gadget/file_storage.c
>> @@ -1696,6 +1696,8 @@ static int do_read_toc(struct fsg_dev *fsg, struct fsg_buffhd *bh)
>>   	int		msf = fsg->cmnd[1]&  0x02;
>>   	int		start_track = fsg->cmnd[6];
>>   	u8		*buf = (u8 *) bh->buf;
>> +	u8		format;
>> +	int		ret;
>>
>>   	if ((fsg->cmnd[1]&  ~0x02) != 0 ||		/* Mask away MSF */
>>   			start_track>  1) {
>> @@ -1703,18 +1705,22 @@ static int do_read_toc(struct fsg_dev *fsg, struct fsg_buffhd *bh)
>>   		return -EINVAL;
>>   	}
>>
>> -	memset(buf, 0, 20);
>> -	buf[1] = (20-2);		/* TOC data length */
>> -	buf[2] = 1;			/* First track number */
>> -	buf[3] = 1;			/* Last track number */
>> -	buf[5] = 0x16;			/* Data track, copying allowed */
>> -	buf[6] = 0x01;			/* Only track is number 1 */
>> -	store_cdrom_address(&buf[8], msf, 0);
>> +	/*
>> +	 * Check if CDB is old style SFF-8020i
>> +	 * i.e. format is in 2 MSBs of byte 9
>> +	 * Mac OS-X host sends us this.
>> +	 */
>> +	format = (fsg->cmnd[9]>>  6)&  0x3;
>> +	if (format == 0)
>> +		format = fsg->cmnd[2]&  0xf;	/* new style MMC-2 */
>
> The spec says: "Format field definition: When Format in Byte 2 is zero,
> then Byte 9 is used."  This logic does not follow that description.
>

Yes indeed. I'll fix all this in v2. Thanks for review.

-- 
regards,
-roger
--
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