Thus spake Kai Makisara ([EMAIL PROTECTED]):
> On Thu, 20 Nov 2003, Alan Stern wrote:
>
...
> > The answer seems very simple. There should be a host template entry for
> > dma buffer alignment (there's already a dma_boundary member). It would be
> > copied into the device's request queue stucture if it is nonzero,
> > overriding the default value of 512. sg and st should check the user
> > buffer against the request queue's dma_alignment mask and avoid doing
> > direct I/O if the alignment is wrong -- just fall back to normal I/O.
> >
> > Any objections to this scheme?
> >
> My only objection is the default. It should be zero. If I read the
> usb-storage sources correctly, the scsi_host_template is defined in one
> file (scsiglue.c). If the mask is there set to 511, all USB storage
> devices get 512-byte alignment and other get no constraints. All get
> optimal result with minimal work. (Adding the check to st and sg is
> trivial.)
>
To make this a little more than talk, here is a patch for 2.6.0-test9 plus
csets up to today (compiled and tested but does not include the check for sg):
---8<---
diff -ur linux-2.6-cset/drivers/scsi/st.c linux-2.6-cset-k/drivers/scsi/st.c
--- linux-2.6-cset/drivers/scsi/st.c 2003-09-09 18:19:45.000000000 +0300
+++ linux-2.6-cset-k/drivers/scsi/st.c 2003-11-20 20:49:25.000000000 +0200
@@ -1267,7 +1267,8 @@
i = STp->try_dio && try_rdio;
else
i = STp->try_dio && try_wdio;
- if (i) {
+
+ if (i && ((unsigned int)buf & STp->device->host->hostt->dma_align_mask) == 0) {
i = st_map_user_pages(&(STbp->sg[0]), STbp->use_sg,
(unsigned long)buf, count, (is_read ? READ :
WRITE),
STp->max_pfn);
diff -ur linux-2.6-cset/drivers/usb/storage/scsiglue.c
linux-2.6-cset-k/drivers/usb/storage/scsiglue.c
--- linux-2.6-cset/drivers/usb/storage/scsiglue.c 2003-10-25 22:35:58.000000000
+0300
+++ linux-2.6-cset-k/drivers/usb/storage/scsiglue.c 2003-11-20 19:34:56.000000000
+0200
@@ -312,6 +312,9 @@
/* lots of sg segments can be handled */
.sg_tablesize = SG_ALL,
+ /* alignment to 512-byte required */
+ .dma_align_mask = 0x1ff,
+
/* merge commands... this seems to help performance, but
* periodically someone should test to see which setting is more
* optimal.
Only in linux-2.6-cset/include/asm: page.h~
Only in linux-2.6-cset/include/asm-i386: page.h~
diff -ur linux-2.6-cset/include/scsi/scsi_host.h
linux-2.6-cset-k/include/scsi/scsi_host.h
--- linux-2.6-cset/include/scsi/scsi_host.h 2003-10-25 22:35:58.000000000 +0300
+++ linux-2.6-cset-k/include/scsi/scsi_host.h 2003-11-20 19:33:32.000000000 +0200
@@ -268,6 +268,12 @@
unsigned long dma_boundary;
/*
+ * Alignment mask for scatter/gather segments. The offset and'ed
+ * with the mask must be zero for segments.
+ */
+ unsigned int dma_align_mask;
+
+ /*
* This specifies "machine infinity" for host templates which don't
* limit the transfer size. Note this limit represents an absolute
* maximum, and may be over the transfer limits allowed for
---8<---
--
Kai
-------------------------------------------------------
This SF.net email is sponsored by: SF.net Giveback Program.
Does SourceForge.net help you be more productive? Does it
help you create better code? SHARE THE LOVE, and help us help
YOU! Click Here: http://sourceforge.net/donate/
_______________________________________________
[EMAIL PROTECTED]
To unsubscribe, use the last form field at:
https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
