On Mon, May 11, 2020 at 09:32:47PM +0300, Serge Semin wrote:

Thanks for the explanation. Max segment size being set to the DMA controller generic
device should work well. There is no need in setting the transfer and messages
size limitations. Besides I don't really see the
max_transfer_size/max_message_size callbacks utilized in the SPI core. These
functions are called in the spi-mem.c driver only. Do I miss something?

We really should validate them in the core but really they're intended
for client drivers (like spi-mem kind of is) to allow them to adapt the
sizes of requests they're generating so the core never sees anything
that's too big.  For the transfers we have a spi_split_transfers_maxsize()
helper if anything wants to use it.  Fortunately there's not that many
controllers with low enough limits to worry about so actual usage hasn't
been that high.