Re: [PATCH] zorro_esp: increase maximum dma length to 65536 bytes

[James Bottomley <jejb@linux.ibm.com>]

On Sun, 2019-11-10 at 15:36 +1300, Michael Schmitz wrote:
> All of the old board-specific drivers used a max transfer length of 
> 0x1000000, only the fastlane driver used 0xfffc. That lower limit
> might be due to a DMA limitation on the fastlane board. We could
> accommodate  the different limit for this board by using a board-
> specific  dma_length_limit() callback...

Sure, that implies the minimum dma burst length is 4 bytes ...

> > case for any of the cards the zorro_esp drives, it might be better
> > to lower the max length to 61440 (64k-4k) so the residual is a
> > page.
> 
> For the benefit of keeping the code simple, and avoid retesting the 
> fastlane board, that might indeed be the better solution.

... which means you don't have to lower the limit by 4k as I suggested,
 because I was being incredibly conservative about what the dma burst
length might be, just use 0xfffc as the default.  I think raising to
0x1000000 for boards which can support it is fine too if you want to
add the extra logic to the driver.

James