On Sat, 2019-11-09 at 20:14 +0100, Kars de Jong wrote:
When using this driver on a Blizzard 1260, there were failures whenever DMA transfers from the SCSI bus to memory of 65535 bytes were followed by a DMA transfer of 1 byte. This caused the byte at offset 65535 to be overwritten with 0xff. The Blizzard hardware can't handle single byte DMA transfers. Besides this issue, limiting the DMA length to something that is not a multiple of the page size is very inefficient on most file systems. It seems this limit was chosen because the DMA transfer counter of the ESP by default is 16 bits wide, thus limiting the length to 65535 bytes. However, the value 0 means 65536 bytes, which is handled by the ESP and the Blizzard just fine. It is also the default maximum used by esp_scsi when drivers don't provide their own dma_length_limit() function.
Have you tested this on any other hardware? the reason most legacy hardware would have a setting like this is because they have a two byte transfer length register and zero doesn't mean 65536. If this is the 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. James
