Re: [PATCH 5/8] dma: dw: Avoid partial transfers

Andy Shevchenko
2022-02-20T10:50:50Z

On Fri, Feb 18, 2022 at 07:12:23PM +0100, Miquel Raynal wrote:
> From: Phil Edworthy <phil.edworthy@renesas.com>
>
> Pausing a partial transfer only causes data to be written to mem that is
> a multiple of the memory width setting.
>
> However, when a DMA client driver finishes DMA early, e.g. due to UART
> char timeout interrupt, all data read from the DEV must be written to MEM.
>
> Therefore, allow the slave to limit the memory width to ensure all data
> read from the DEV is written to MEM when DMA is paused.

Is this a fix?
What happens to the data if you don't do this?
As far as I understood the Synopsys DesignWare specification the DMA controller
is capable of flushing FIFO in that case on byte-by-byte basis. Do you have an
HW integration bug?

TL;DR: tell us more about this.

...

> + if (sconfig->dst_addr_width && sconfig->dst_addr_width < data_width)
> + data_width = sconfig->dst_addr_width;

But here no check that you do it for explicitly peripheral to memory, so this
will affect memory to peripheral transfers as well.

--
With Best Regards,
Andy Shevchenko