Re: sata_nv and dynamically changing DMA mask?

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Alan Cox wrote:
On Mon, 29 Oct 2007 22:17:40 -0600
Robert Hancock <hancockr@xxxxxxx> 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-ide" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[Index of Archives]     [Linux Filesystems]     [Linux SCSI]     [Linux RAID]     [Git]     [Kernel Newbies]     [Linux Newbie]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Samba]     [Device Mapper]

  Powered by Linux