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.
*/
unsigned short max_sectors;
>
-
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