[PATCH RFC 1/2] MUSB: CPPI 4.1 DMA driver (take 4)
Russell King - ARM Linux
linux at arm.linux.org.uk
Mon Nov 2 06:54:58 EST 2009
On Mon, Nov 02, 2009 at 04:27:59PM +0530, Gupta, Ajay Kumar wrote:
> > On Mon, Nov 02, 2009 at 09:51:13AM +0530, Gupta, Ajay Kumar wrote:
> > > Is there any updated patch on cppi4.1 core also?
> >
> > Is there _any_ cppi4.1 core patch anywhere? Not according to google.
>
> Russell,
>
> Here is the latest version of cppi4.1 core.
> http://patchwork.kernel.org/patch/46698/
A few points come up about this.
1. alloc_queue() - this is a find_next_zero_bit loop coupled with a
check for the excluded bitmap.
end = start + count;
do {
bit = find_next_zero_bit(allocated, end, start);
if (bit >= end)
return -ENOSPC;
start = bit + 1;
} while (test_bit(bit, excluded));
__set_bit(bit, allocated);
return bit;
Note that 'allocated' and 'excluded' both need to be arrays of
unsigned long.
2. alloc_queue() again - it looks to me like the existing implementation
is racy - who ensures that we don't have two people searching and
allocating the same bit? A solution to that without adding locking
would be:
end = start + count;
do {
bit = find_next_zero_bit(allocated, end, start);
if (bit >= end)
return -ENOSPC;
start = bit + 1;
} while (test_bit(bit, excluded) || test_and_set_bit(bit, allocated));
return bit;
3. linking_ram - cppi41_queue_mgr_init() seems to be the only user. I
don't see why linking_ram would be necessary.
4. debugging printks via pr_debug() please (and define DEBUG at the top of
the file to enable debugging.)
> > If it's a USB DMA device (from the patches I can find, that seems to be
> > the case) then why can't it live in drivers/usb or drivers/dma ?
>
> CPPI4.1 DMA engine can be used either by USB or by Ethernet interface though
> currently only USB is using it but in future even Ethernet devices may use it.
drivers/dma does seem to be the right place for this.
More information about the linux-arm-kernel
mailing list