On Thu, 31 Jan 2008 17:58:30 -0800 Nicholas A. Bellinger wrote:
> On Thu, 2008-01-31 at 13:42 -0600, James Bottomley wrote:
> > On Thu, 2008-01-31 at 10:44 -0800, Nicholas A. Bellinger wrote:
> > > > In short, and to repeat: almost every internal size counter to block is
> > > > in units of 512 byte sectors ... that includes capacity, maximum etc ...
> > > >
> > >
> > > Ok, after reading your followup with Geert I see that this looks like a
> > > bug in ps3rom.c assuming 2048 byte sectors to calculate .max_sectors
> > > (which was originally set to 32 as I mentioned). Using the setting
> > > BOUNCE_SIZE << 9 where BOUNCE_SIZE is the request size in bytes looks
> > > like this will solve the issue. My misunderstanding was
> > > that .max_sectors was allowed to be calcuated in non 512 byte sectors,
> > > so please disregard my patch.
> > >
> > > Geert, .max_sectors for ps3rom.c using 512 byte sectors ends up being
> > > 128, yes.?
> > >
> > > James, could we put something in the SCSI docs stating that .max_sectors
> > > MUST be calculated against 512 byte sectors..?
> >
> > If that "we" is royal, then certainly you're welcome to submit a patch
> > (just get Randy's ack). However, do take a look at the existing docs
> > first. Certainly the block layer seems to make this very clear:
> >
> > /**
> > * blk_queue_max_sectors - set max sectors for a request for this queue
> > * @q: the request queue for the device
> > * @max_sectors: max sectors in the usual 512b unit
> > ^^^^^^^^^^^^^^^^^^^^^^
> > *
> > * Description:
> > * Enables a low level driver to set an upper limit on the size of
> > * received requests.
> > **/
> >
>
> Agreed, here is the patch to make this clear within SCSI. Randy, does
> this look OK..?
>
> Thanks,
>
> --nab
>
> Signed-off-by: Nicholas A. Bellinger <nab@xxxxxxxxxxxxxxx>
>
> diff --git a/Documentation/scsi/scsi_mid_low_api.txt b/Documentation/scsi/scsi_mid_low_api.txt
> index 6f70f2b..570f271 100644
> --- a/Documentation/scsi/scsi_mid_low_api.txt
> +++ b/Documentation/scsi/scsi_mid_low_api.txt
> @@ -1244,13 +1244,12 @@ of interest:
> this_id - scsi id of host (scsi initiator) or -1 if not known
> sg_tablesize - maximum scatter gather elements allowed by host.
> 0 implies scatter gather not supported by host
> - max_sectors - maximum number of sectors (usually 512 bytes) allowed
> - in a single SCSI command. The default value of 0 leads
> - to a setting of SCSI_DEFAULT_MAX_SECTORS (defined in
> - scsi_host.h) which is currently set to 1024. So for a
> - disk the maximum transfer size is 512 KB when max_sectors
> - is not defined. Note that this size may not be sufficient
> - for disk firmware uploads.
> + max_sectors - maximum number of 512 bytes sectors allowed in a single
> + SCSI command. The default value of 0 leads to a setting
> + of SCSI_DEFAULT_MAX_SECTORS (defined in scsi_host.h) which
> + is currently set to 1024. So for a disk the maximum transfer
> + size is 512 KB when max_sectors is not defined. Note that
> + this size may not be sufficient for disk firmware uploads.
> cmd_per_lun - maximum number of commands that can be queued on devices
> controlled by the host. Overridden by LLD calls to
> scsi_adjust_queue_depth().
> diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
> index 5c58d59..84098e3 100644
> --- a/include/scsi/scsi_host.h
> +++ b/include/scsi/scsi_host.h
> @@ -372,7 +372,10 @@ struct scsi_host_template {
> unsigned short sg_tablesize;
>
> /*
> - * If the host adapter has limitations beside segment count
> + * If the host adapter has limitations beside segment count.
> + * Note that this value MUST be calculated in 512 byte sectors,
> + * even if the attached struct scsi_device->sector_size is expected
> + * to use non 512 byte sectors.
How about:
* to use a sector size other than 512 bytes.
and
Acked-by: Randy Dunlap <randy.dunlap@xxxxxxxxxx>
> */
> unsigned short max_sectors;
---
~Randy
-
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