Re: [PATCH] OMAP: fix DMA vs memory ordering

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

 



On Saturday 14 April 2012 06:54 PM, Russell King - ARM Linux wrote:
> Using coherent DMA memory with the OMAP DMA engine results in
> unpredictable behaviour due to memory ordering issues; as things stand,
> there is no guarantee that data written to coherent DMA memory will be
> visible to the DMA hardware.
> 
> This is because the OMAP dma_write() accessor contains no barriers,
> necessary on ARMv6 and above.  The effect of this can be seen in comments
> in the OMAP serial driver, which incorrectly talks about cache flushing
> for the coherent DMA stuff.
> 
> Rather than adding barriers to the accessors, add it in the DMA support
> code just before we enable DMA, and just after we disable DMA.  This
> avoids having barriers for every DMA register access.
> 
> Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
> ---
I don't why the synchronisation in dma_[start/stop] was
missing. The patch indeed make complete sense.



> Is this why no one uses DMA with the serial driver?
>
Will check if this patch helps in some of the DMA issues
seen in serial driver.

Regards
Santosh
--
To unsubscribe from this list: send the line "unsubscribe linux-omap" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html


[Index of Archives]     [Linux Arm (vger)]     [ARM Kernel]     [ARM MSM]     [Linux Tegra]     [Linux WPAN Networking]     [Linux Wireless Networking]     [Maemo Users]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite Trails]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux