lkml.org 
[lkml]   [2015]   [Apr]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] dmaengine: bcm2835: Add slave dma support
From
Date

> On 15.04.2015, at 11:56, Noralf Trønnes <noralf@tronnes.org> wrote:
> +#define MAX_LITE_TRANSFER (SZ_64K - 1)
> +#define MAX_NORMAL_TRANSFER SZ_1G
...
> + if (c->ch >= 8) /* LITE channel */
> + max_size = MAX_LITE_TRANSFER;
> + else
> + max_size = MAX_NORMAL_TRANSFER;
> + period_len = min(period_len, max_size);
> + d->frames = (buf_len - 1) / (period_len + 1);

I wonder if it is wise to split the transfers on 65535 bytes for the
Lite DMA-channels - especially if you are transferring to word size
registers (like SPI_FIFO), you still push 16384 words into the register
and the last word of this transfer (word 16384) still is assumed 4 valid
bytes by the device and thus gets operated upon - even if the last byte
contains garbage from the DMA-transfer point of view.

So maybe it is better to separate on SZ_64K-4 or better still SZ_32K to
be on a power of 2 address boundary.

\
 
 \ /
  Last update: 2015-04-15 18:01    [W:0.565 / U:0.080 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site