Alan Cox wrote:
On Mon, 29 Oct 2007 22:17:40 -0600
Robert Hancock <[email protected]> wrote:
In the sata_nv driver, when running in ADMA mode, we can do 64-bit DMA.
However, when an ATAPI device like a DVD drive is connected, we can't
use ADMA mode, and so we have to abide by the restrictions of a normal
SFF ATA controller and can only do 32-bit DMA. We detect this and try to
set the blk_queue_bounce_limit, blk_queue_segment_boundary and
blk_queue_max_hw_segments to the values corresponding to a normal SFF
controller.
What about the DMA padding buffer from nv_adma_port_start and internal
buffers for commands like request sense that don't come via the request
queue directly.
Indeed we do call ata_port_start from nv_adma_port_start, which calls
dmam_alloc_coherent to allocate the SFF PRD table. Since the DMA mask is
64-bit, this could indeed be allocated above 4GB which would be bad.
I suppose what we could do is just not call ata_port_start there, but
move it into nv_adma_slave_config and call it when going into non-ADMA
mode. We'd have to drop the DMA mask down to 32-bit first as well as
setting blk_queue_bounce_limit though, which is one of my questions, is
this OK to do?
Also it seems nv_adma_use_reg_mode() can decide to send other commands
via the non ADMA interface even for ATA devices. Are we 100% certain it
never decides to let through a command with DMA via the register
interface in this case - what do you see if you instrument the function ?
The only cases where that could happen are for polling DMA commands
(which I presume we never do) or where result taskfile is requested. The
latter could be a problem for ATA passthrough commands using DMA, I
suppose.. Question is what we can do about it.. We have to switch out of
ADMA mode to read a result taskfile. I guess that's not really a problem
unless somebody starts issuing NCQ commands via ATA pass-through. Do we
allow that?
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
