Re: [PATCH v3] Re: another unusual flag for a really limited device

On Wed, 28 Nov 2007 13:42:00 CST, Doug Maxey wrote:
> 
> On Wed, 28 Nov 2007 14:31:27 EST, Alan Stern wrote:
> > On Wed, 28 Nov 2007, Doug Maxey wrote:
> >
> > > +	/* And at least one more device needs an even smaller max.
> > > +	 * When testing the native PAGE_SIZE, clamp at 8k.  No need
> > > +	 * allow a 64K or even 16M page in there.
> > > +	 */
> >
> > Why not combine the code for the two flags, as shown in the partial
> > patch below?
> >
> > Also, trying to clamp at 8 KB is futile.
> 
> Alright.  I was thinking of the remote possibility that the platform
> could use use something 64k or larger as the native page size, which
> would defeat trying to limit the device.  If there were any other
> devices out there that required this, and the administrator tried to
> stick one in a powerpc, for example, the code would not have the
> desired result.

They lose.  Time for someone to fix the device firmware, or just not 
use on that class of platform.

> 
> > Read the source code for
> > blk_queue_max_sectors() in drivers/block/ll_rw_blk.c and you'll see.
> 
> will do.

Indeed, it does clamp the lower limit at PAGE_CACHE_SIZE regardless.  
Is the below going upstream, and I just drop my chunk?

Or, do you want me to fold this in?

> 
> >
> > Alan Stern
> >
> >
> > Index: usb-2.6/drivers/usb/storage/scsiglue.c
> > ===================================================================
> > --- usb-2.6.orig/drivers/usb/storage/scsiglue.c
> > +++ usb-2.6/drivers/usb/storage/scsiglue.c
> > @@ -113,10 +113,19 @@ static int slave_configure(struct scsi_d
> >  	/* Many devices have trouble transfering more than 32KB at a time,
> >  	 * while others have trouble with more than 64K. At this time we
> >  	 * are limiting both to 32K (64 sectores).
> > +	 *
> > +	 * Some other devices have trouble transferring even that much.
> > +	 * We'll limit them to PAGE_CACHE_SIZE, which is the minimum.
> >  	 */
> > -	if ((us->flags & US_FL_MAX_SECTORS_64) &&
> > -			sdev->request_queue->max_sectors > 64)
> > -		blk_queue_max_sectors(sdev->request_queue, 64);
> > +	if (us->flags & (US_FL_MAX_SECTORS_64 | US_FL_MAX_SECTORS_MIN)) {
> > +		unsigned int max_sectors = 64;
> > +
> > +		if (us->flags & US_FL_MAX_SECTORS_MIN)
> > +			max_sectors = PAGE_CACHE_SIZE >> 9;
> > +		if (sdev->request_queue->max_sectors > max_sectors)
> > +			blk_queue_max_sectors(sdev->request_queue,
> > +					max_sectors);
> > +	}
> >
> >  	/* We can't put these settings in slave_alloc() because that gets
> >  	 * called before the device type is known.  Consequently these
> >
> 
> 
> 
> 



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