Linux scsi / usb-mass-storage and HP printer cardreader bug + fix

[Boaz Harrosh]

On Thu, Jan 10 2008 at 12:52 +0200, Hans de Goede <j.w.r.degoede at hhs.nl> wrote:
> Boaz Harrosh wrote:
>> ----- Original Message -----
>> *From:* Hans de Goede <j.w.r.degoede at hhs.nl>
>> *To:* USB Storage list <usb-storage at lists.one-eyed-alien.net>
>> *CC:* fedora-kernel-list at redhat.com, USB development list
>> <linux-usb-devel at lists.sourceforge.net>, David Brown
>> <usb-storage2 at davidb.org>, Guillaume Bedot <littletux at zarb.org>,
>> linux-scsi at vger.kernel.org, linux-usb at vger.kernel.org
>> *Sent:* Wed, Jan 09 2008 at 23:44 +0200
>> *Subject:* Linux scsi / usb-mass-storage and HP printer cardreader bug + fix
>>
>>
>>> Hi All,
>>>
>>> First of all sorry for the somewhat massive cross-posting, I've spend a 
>>> significant amount of time hunting down this bug, and so far the response has 
>>> been less the overwhelming.
>>>
>>> The problem is with the HP PSC 1350 (my printer and confirmed by 2 others) and 
>>> atleast also the HP PSC 1610 (confirmed by Guillaume Bedot, in the CC).
>>>
>>> The cardreader of the multi function printers will "crash" and from that moment 
>>> on no longer communicate in any sane way, if you try to read the last sector of 
>>> an sdcard* in a read that is more then 1 sector, so trying to read 8 sectors 
>>> starting at sector capicity-8 will crash it, as will reading 2 sectors starting 
>>> at sector capicity-2, however reading the last sector in a one 1 sector read 
>>> will succeed! (* xdcards seem to be fine).
>>>
>>> I haven't tried if it will crash on larger then 1 sector writes which include 
>>> the last sector too, I immediately added code to not do that in both the read 
>>> and write paths. I have tested reading and writing the end of the disk with 
>>> this kludge in and it works.
>>>
>>> I currently have a somewhat ugly proof of concept patch for this, which adds 
>>> another type of usb-massstorage quirk. When this quirk flag is set, the 
>>> usb-massstorage driver modifies READ_10 and WRITE_10 commands of more then 1 
>>> sector which includes the last sector to become one sector less. I've been told 
>>> by scsi subsystem developers that doing a shorter read / write then requested 
>>> is not a problem, the scsi subsystem is designed to handle getting less then it 
>>> asked for and will send a seperate request for the last sector.
>>>
>>> I and 3 others (2 on a PSC 1350 too, one on a PSC1610) have tested this patch 
>>> with success. I'm not asking for this patch to be included to the kernel as is, 
>>> I'm asking for the now known workaround for this to be added to the kernel in 
>>> someway!
>>>
>>> Perhaps its an idea to add the posibility to have a scsi command filter 
>>> function / callback to the scsi or usb-massstorage subsystem, and then add a 
>>> mechanism to set this filter depending on usb id's and if added to the scsi 
>>> layer, a mechanism to set it based on scsi device and manufacturer 
>>> identification strings. Such a mechanism might be usefull in the future to work 
>>> around other broken hardware too, and has the added advantage of not having 
>>> todo much changes to the normal code path, keep that readable.
>>>
>>> I'm willing to come up with a patch for such a filter mechanism, provided I get 
>>> some pointers where this is best added.
>>>
>>> Thanks & Regards,
>>>
>>> Hans
>>>
>>>
>>> p.s.
>>>
>>> I've also included the fedora-kernel list in the addressee's because I was 
>>> hoping that maybe someone can take one of these printers to the kernel hackfest 
>>>    in the weekend's fudcon and take a look at this.
>>>   
>>> +		if ((offset + num) == sdkp->capacity && num > 1) {
>>> +			if (srb->cmnd[8] == 0)
>>> +				srb->cmnd[7]--;
>>> +			srb->cmnd[8]--;
>>> +			srb->request_bufflen -= 512;
>>> +			srb->underflow -= 512;
>>> +		}
>>>   
>> This will no longer compile on top of latest scsi-misc, and
>> LLDs are not suppose to modify request_bufflen anymore.
>>
>> I'm not sure what the proper solution should be?
>>
> 
> I guess the proper solution would be to add a special case to the scsi layer 
> where the read10 / write10 command is issued, and split the request in 2 there 
> when it involves the last sector.
> 
> There was another reply in this thread stating that problems reading the last 
> sector with sd / mmc cards happen quite often, and that this is most likely not 
> an isolated case.
> 
> Regards,
> 
> Hans

Yes, you're right. in ULDs it is a much proper way to do this.

So I guess you'll have to do that special host flag or device
flag, and add a check for it in sd.c. You'll see that sd.c is 
already doing bufflen truncation at sd_prep_fn(), just add one
more case.

Boaz