On Wed, Jul 18, 2018 at 11:47:30AM -0500, David Lechner wrote: > On 7/18/18 10:04 AM, Mark Brown wrote:
> > This feels like it should have a soft implementation if it is going to > > be truly usable, the vast majority of SPI controllers don't do this and > This occurred to me as well. Another possibility, though, would be to leave > it up to the client device drivers to support both cases, e.g.: > if (master has SPI_CS_WORD support) > setup message as single transfer > else > setup message as multiple one-word transfers > This seems like that would be more efficient than having a generic > implementation for masters that says: That then requires every single user to open code this which immediately suggests that there should be a helper which is going to look a lot like any generic implementation. > if (master does not have SPI_CS_WORD support) > allocate enough transfers for each word of each > each transfer of the message > allocate and setup a new message for these transfers > loop through the original transfers of the original > message and copy them to the new transfers > send the new message > free allocated message and transfers I'd imagine that the much bigger problem is that you end up with enormous numbers of operations for any non-trivial transfers which is going to happen anyway. It's really only the copying bit that's at all an overhead here. > > I can only think of a few that have the hardware feature. I'd also > > expect to see some validation added to the core spi_setup() since at > > present a client driver could set the mode option but then have it > > ignored by the controller which would presumably break things, we > > currently only have checks for specific modes and nothing that'd catch > > an unknown flag like this. > There is already a generic mode flags check in spi_setup() that will catch > this and return an error if the device has the SPI_CS_WORD flag set and the > controller does not. (I know this works because I ran into it during > development.) Ah, good - I'd forgotten it was there and didn't spot it when I went to check.
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