Hi Marek,
On Mon, Feb 27, 2012 at 9:11 AM, Marek Vasut marex@denx.de wrote:
Hi Marek,
On Mon, Feb 27, 2012 at 8:49 AM, Marek Vasut marex@denx.de wrote:
As DMA expects the buffers to be equal and larger then cache lines, This aligns buffers at cacheline.
Signed-off-by: Puneet Saxena puneets@nvidia.com Signed-off-by: Jim Lin jilin@nvidia.com
First of all, thanks for this patch, it really helps. But, there are a few things that concern me.
Changes for V2: - Use "ARCH_DMA_MINALIGN" directly - Use "ALIGN" to align size as cacheline - Removed headers from usb.h - Send 8 bytes of device descriptor size to read Max packet size scsi.h header is needed to avoid extra memcpy from local buffer to global buffer.
common/cmd_usb.c | 3 +- common/usb.c | 61 ++++++++++++++++++++++++------------------ common/usb_storage.c | 59 +++++++++++++++++++---------------------- disk/part_dos.c | 2 +- drivers/usb/host/ehci-hcd.c | 8 +++++ include/scsi.h | 4 ++- 6 files changed, 77 insertions(+), 60 deletions(-)
diff --git a/common/cmd_usb.c b/common/cmd_usb.c index 320667f..bca9d94 100644 --- a/common/cmd_usb.c +++ b/common/cmd_usb.c @@ -150,7 +150,8 @@ void usb_display_class_sub(unsigned char dclass, unsigned char subclass,
void usb_display_string(struct usb_device *dev, int index) {
- char buffer[256];
- ALLOC_CACHE_ALIGN_BUFFER(char, buffer, 256);
Why not memalign(), do you want to allocate on stack so badly ?
This issue came up with MMC and there was a strong request not to sprinkle the code with malloc. In fact the macro above was devised at some cost just to solve this problem.
This is really weird solution :-(
It's not pretty under the hood but it solves the problem well for MMC. Apart from the alignment of buffers, it is as efficient as the original code.
[snip]
{ int tries;
- struct usb_port_status portsts;
- ALLOC_CACHE_ALIGN_BUFFER(struct usb_port_status, portsts, 1);
Looking at all this stuff, it's already allocated on stack. Ok, I already outlined first option -- memalign(), but that'd really put quite a strain on the memory allocator -- the other option (and maybe even better) is to use __attribute__((aligned)), which will allow the compiler to reorder data allocated on the stack so the array you create is aligned and not much space around on the stack is wasted. Apparently, ALLOC_CACHE_ALIGN_BUFFER() wastes a lot of space on the stack.
There was quite a bit of discussion about this related to MMC. I think the current solution is the result of that discussion...
Can you please point me to such discussion?
Start here perhaps and look at the whole thread:
http://lists.denx.de/pipermail/u-boot/2011-August/099152.html
Thanks!
Regards, Simon