[U-Boot] [PATCH v3 1/3] USB: make usb_kbd obey USB DMA alignment requirements

[Stephen Warren]

On 10/23/2012 03:37 PM, Allen Martin wrote:
> Change usb_kbd driver to obey alignment requirements for USB DMA on
> the buffer used for data transfer.  This is necessary for
> architectures that enable dcache and enable USB DMA.

> diff --git a/common/usb_kbd.c b/common/usb_kbd.c

> +/*
> + * This structure must be aligned to USB_DMA_MINALIGN to allow DMA to
> + * buffer "new" below.
> + */
>  struct usb_kbd_pdata {
> +	uint8_t		new[8];
> +	uint8_t		old[8];

Oh, one more thought on this: Those fields should both be aligned, and
their size be aligned too, at least to cache size. In particular, if we
have HW write to new[], then invalidate the cache that contains new[]
because it just did, we want to make sure that fields after new[] (i.e.
old[], ...) don't get invalidate too, in case the cache contained stale
data for those fields. That's one of the things that the (stack-based)
ALLOC_CACHE_ALIGN_BUFFER handles. Perhaps make those two fields
pointers, and point those at a memalign()-allocated blob, where the size
of those blobs are something like ROUND_UP(USB_DMA_MINALIGN, 8)?

Sorry for forgetting about this before!