On 11/15/2017 03:17 PM, Goldschmidt Simon wrote:
> Bounce buffer may be used for CPU-only transfers (this is currently
> the case for cadence_qspi). However, in this case, invalidating the
> data cache might throw away copied data that is still in the cache
> only.
>
> To make CPU-only transfers work with bouncebuf (but still take
> advantage of having aligned buffers), a new flag 'GEN_BB_NODMA' is
> introduced. If this flag is set, cache flushing/invalidation is
> skipped and only the alignment part of bouncebuf is active.
>
> Signed-off-by: Simon Goldschmidt <sgoldschm...@de.pepperl-fuchs.com>
Why don't you just fix the cache operations in the driver ?
This bounce-buffer for only CPU operations is just wasting CPU cycles
and degrades performance and I just cannot find a good reason for it.
> ---
> common/bouncebuf.c | 9 +++++----
> include/bouncebuf.h | 9 +++++++++
> 2 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/common/bouncebuf.c b/common/bouncebuf.c
> index 054d9e0302..0d18477f13 100644
> --- a/common/bouncebuf.c
> +++ b/common/bouncebuf.c
> @@ -55,16 +55,17 @@ int bounce_buffer_start(struct bounce_buffer *state, void
> *data,
> * Flush data to RAM so DMA reads can pick it up,
> * and any CPU writebacks don't race with DMA writes
> */
> - flush_dcache_range((unsigned long)state->bounce_buffer,
> - (unsigned long)(state->bounce_buffer) +
> - state->len_aligned);
> + if (!(state->flags & GEN_BB_NODMA))
> + flush_dcache_range((unsigned long)state->bounce_buffer,
> + (unsigned long)(state->bounce_buffer) +
> + state->len_aligned);
>
> return 0;
> }
>
> int bounce_buffer_stop(struct bounce_buffer *state)
> {
> - if (state->flags & GEN_BB_WRITE) {
> + if ((state->flags & (GEN_BB_WRITE|GEN_BB_NODMA)) == GEN_BB_WRITE) {
> /* Invalidate cache so that CPU can see any newly DMA'd data */
> invalidate_dcache_range((unsigned long)state->bounce_buffer,
> (unsigned long)(state->bounce_buffer) +
> diff --git a/include/bouncebuf.h b/include/bouncebuf.h
> index 5ffa99bc13..c6720b3b2e 100644
> --- a/include/bouncebuf.h
> +++ b/include/bouncebuf.h
> @@ -37,6 +37,15 @@
> */
> #define GEN_BB_RW (GEN_BB_READ | GEN_BB_WRITE)
>
> +/*
> + * GEN_BB_NODMA -- Data is read/written by CPU only (no DMA), so no cache
> + * flushing and invalidating is required. Not passing this for GEN_BB_WRITE
> + * transfers done by the CPU (not DMA) may result in invalid data as the data
> + * written into the cache is lost by invalidating the dcache after the
> transfer
> + * (unless a writethrough cache is used).
> + */
> +#define GEN_BB_NODMA (1 << 2)
> +
> struct bounce_buffer {
> /* Copy of data parameter passed to start() */
> void *user_buffer;
>
--
Best regards,
Marek Vasut
_______________________________________________
U-Boot mailing list
U-Boot@lists.denx.de
https://lists.denx.de/listinfo/u-boot
