lkml.org 
[lkml]   [2008]   [Aug]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH] ieee1394: sbp2: enforce s/g segment size limit
From
On Tue, 12 Aug 2008 10:04:14 -0700
"Grant Grundler" <grundler@google.com> wrote:

> On Sat, Aug 9, 2008 at 11:20 AM, Stefan Richter
> <stefanr@s5r6.in-berlin.de> wrote:
> > 1. We don't need to round the SBP-2 segment size limit down to a
> > multiple of 4 kB (0xffff -> 0xf000). It is only necessary to
> > ensure quadlet alignment (0xffff -> 0xfffc).
> >
> > 2. Use dma_set_max_seg_size() to tell the DMA mapping infrastructure
> > and the block IO layer about the restriction. This way we can
> > remove the size checks and segment splitting in the queuecommand
> > path.
> >
> > This assumes that no other code in the ieee1394 stack uses
> > dma_map_sg() with conflicting requirements. It furthermore assumes
> > that the controller device's platform actually allows us to set the
> > segment size to our liking. Assert the latter with a BUG_ON().
> >
> > 3. Also use blk_queue_max_segment_size() to tell the block IO layer
> > about it. It cannot know it because our scsi_add_host() does not
> > point to the FireWire controller's device.
> >
> > We can also uniformly use dma_map_sg() for the single segment case just
> > like for the multi segment case, to further simplify the code.
> >
> > Also clean up how the page table is converted to big endian.
> >
> > Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
> > ---
> >
> > Applicable after
> > [PATCH update] ieee1394: sbp2: stricter dma_sync
> > [PATCH] ieee1394: sbp2: check for DMA mapping failures
> > from a few minutes ago.
> >
> > drivers/ieee1394/sbp2.c | 106 +++++++++++++---------------------------
> > drivers/ieee1394/sbp2.h | 37 +++++--------
> > 2 files changed, 52 insertions(+), 91 deletions(-)
> ...
> > + for_each_sg(sg, sg, sg_count, i) {
> > + len = sg_dma_len(sg);
> > + if (len == 0)
> > + continue;
> >
> > - orb->misc |= ORB_SET_DATA_SIZE(sg_count);
> > + pt[j].high = cpu_to_be32(len << 16);
> > + pt[j].low = cpu_to_be32(sg_dma_address(sg));
> > + j++;
> > + }
>
> While this code will probably work correctly, I believe if the
> sg_dma_len() returns 0, one has walked off the end of the
> "bus address" list.
>
> pci_map_sg() returns how many DMA addr/len pairs are used
> and that count could (should?) be used when pulling the
> dma_len/addr pairs out of the sg list.

Yeah, from a quick look, seems that this patch wrongly handles
sg_count.

This patch sets scsi_sg_count(sc) to sg_count, right? for_each_sg is
expected to be used with a return value of pci_map_sg.

Then this patch can simply do something like:

for_each_sg(sg, sg, sg_count, i) {
pt[i].high = cpu_to_be32(sg_dma_len(sg) << 16);
pt[i].low = cpu_to_be32(sg_dma_address(sg));
}

\
 
 \ /
  Last update: 2008-08-13 01:47    [from the cache]
©2003-2011 Jasper Spaans