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SubjectRe: [PATCH] dmaengine: omap-dma: Enable packed accesses for cyclic transfers
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Vinod,

On 09/14/2015 03:31 PM, Peter Ujfalusi wrote:
> From: Misael Lopez Cruz <misael.lopez@ti.com>
>
> The L3 throughput can be higher than expected when packed access
> is not enabled. The ratio depends on the number of bytes in a
> transaction and the EMIF interface width.

Can you take a look at this patch?

Thanks,
Péter

> The throughput was measured for the following settings/cases:
>
> * Case 1: Burst size of 64 bytes, packed access disabled
> * Case 2: Burst size of 64 bytes, packed access enabled
> * Case 3: Burst disabled, packed access disabled
>
> Throughput measurements were done during McASP-based audio
> playback on the Jacinto6 EVM using the omapconf tool [1]:
> $ omapconf trace bw -m sdma_rd
>
> ---------------------------------------------------------
> Throughput (MB/s)
> Audio parameters Case 1 Case 2 Case 3
> ---------------------------------------------------------
> 44.1kHz, 16-bits, stereo 1.41 0.18 1.41
> 44.1kHz, 32-bits, stereo 1.41 0.35 1.41
> 44.1kHz, 16-bits, 4-chan 2.82 0.35 2.82
> 44.1kHz, 16-bits, 6-chan 4.23 0.53 4.23
> 44.1kHz, 16-bits, 8-chan 5.64 0.71 5.64
> ---------------------------------------------------------
>
> From above measurements, case 2 is the only one that delivers
> the expected throughput for the given audio parameters. For
> that reason, the packed accesses are now enabled.
>
> It's worth to mention that packed accesses cannot be enabled
> for all addressing modes. In cyclic transfers, it can be
> enabled in the source for MEM_TO_DEV and in dest for DEV_TO_MEM,
> as they use post-increment mode which supports packed accesses.
>
> Peter Ujfalusi:
> From the TRM regarding to this:
> "NOTE: Except in the constant addressing mode, the source or
> destination must be specified as packed for burst transactions
> to occur."
>
> So w/o the packed setting the burst on the MEM side was not
> enabled, this explains the numbers.
>
> [1] https://github.com/omapconf/omapconf
>
> Signed-off-by: Misael Lopez Cruz <misael.lopez@ti.com>
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
> ---
> drivers/dma/omap-dma.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dma/omap-dma.c b/drivers/dma/omap-dma.c
> index 249445c8a4c6..1dfc71c90123 100644
> --- a/drivers/dma/omap-dma.c
> +++ b/drivers/dma/omap-dma.c
> @@ -935,8 +935,12 @@ static struct dma_async_tx_descriptor *omap_dma_prep_dma_cyclic(
> else
> d->ccr |= CCR_SYNC_ELEMENT;
>
> - if (dir == DMA_DEV_TO_MEM)
> + if (dir == DMA_DEV_TO_MEM) {
> d->ccr |= CCR_TRIGGER_SRC;
> + d->csdp |= CSDP_DST_PACKED;
> + } else {
> + d->csdp |= CSDP_SRC_PACKED;
> + }
>
> d->cicr |= CICR_MISALIGNED_ERR_IE | CICR_TRANS_ERR_IE;
>
>



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