Re: [PATCH 5/6] spi: imx: support dynamic burst length for ECSPI DMA mode

[Carlos Song]

> -----Original Message-----
> From: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
> Sent: Wednesday, November 26, 2025 4:31 PM
> To: Carlos Song <carlos.song@xxxxxxx>
> Cc: broonie@xxxxxxxxxx; Frank Li <frank.li@xxxxxxx>; hawnguo@xxxxxxxxxx;
> s.hauer@xxxxxxxxxxxxxx; kernel@xxxxxxxxxxxxxx; festevam@xxxxxxxxx;
> imx@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-spi@xxxxxxxxxxxxxxx
> Subject: [EXT] Re: [PATCH 5/6] spi: imx: support dynamic burst length for ECSPI
> DMA mode
> 
> On 26.11.2025 07:42:36, Carlos Song wrote:
> 
> [...]
> > For example len is 512 *3 + 511. So first transfer using BURST_LENGTH
> > = 512 bytes(auto update 3 times), DMA transfer len = 512 *3, second
> > package BURST_LENGTH = 511 bytes, DMA transfer len = 511.(If here we
> > use 512 bytes as BURST_LENGTH, SPI will shift out/in extra bits, it
> > previous isn't acceptable!)
> 
> What happens if you keep the Burst Length at 512 and only transfer 511 bytes
> with the DMA engine?
> 

Sorry for missing one question:
BURST_LENGTH = 511, ECSPI will shift out 511 bytes in bus.
BURST_LENGTH = 512, ECSPI will shift out the last one word all bit in 32 bits FIFO. 
So ECSPI will shift out 512 bytes include 8-bits zero bytes in bus.

Carlos

> Marc
> 
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