Re: [PATCH v3 8/9] spi: rockchip: modify DMA max burst to 1

From: Shawn Lin
Date: Thu Sep 03 2015 - 09:42:01 EST

On 2015/9/3 20:54, Mark Brown wrote:
On Tue, Sep 01, 2015 at 05:58:44PM +0800, Shawn Lin wrote:

Generic dma controller on Rockchips' platform cannot support
DMAFLUSHP instruction which make dma to flush the req of non-aligned
or non-multiple of what we need. That will cause an unrecoverable
dma bus error. The saftest way is to set dma max burst to 1.

If this is a quirk of the DMA controller why is it being fixed with a
property specific to the SPI controller? Can't the DMA controller just
override the burst size?

Cool...that's a good question. Actually DMA controller can't do that since block peripheral controller(e.g sd/emmc, they always access data by block-512Bytes.) can't meet the case. So It's hard for dma controller know who is the caller, and what should be done.

The only thing dma controller can do is avoid to execute DMAFLUSHP on its own. But how about peripheral controller trigger non-multiple access? So that's what I mentioned on covery letter that we should do "broken things" for both dma controller and some peripherals.

+#define ROCKCHIP_SPI_BORKEN_BURST_LEN (1<<0) /* broken burst len*/

This is misspelt.

Woops, sorry for the bit. Thanks, Mark.

Best Regards
Shawn Lin

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