On Mon, May 25, 2020 at 01:17:01PM +0200, Marc Kleine-Budde wrote: > On 5/21/20 10:19 PM, Tim Harvey wrote: > > > Should I be submitting this patch with logic that only does > > half-duplex if the spi controller doesn't support it (if > > (spi->controller->flags & SPI_CONTROLLER_HALF_DUPLEX)) or is it > > acceptable to simply make the driver half-duplex like this for all > > cases? > Please make half duplex transfers depending on SPI_CONTROLLER_HALF_DUPLEX as > most drivers have a considerable overhead at the end of a transfer. > Most of them wait for a transfer complete interrupt. Which might take longer > than the actual SPI transfer. Splitting one full duplex read-register transfer > (which is a write followed by a read) into two half duplex transfers would kill > performance on full duplex capable controllers. This isn't something that every individual driver should be doing, such rewriting should happen in the core so that everything sees the benefit.
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