Re: [PATCH] can: mcp251x: convert to half-duplex SPI

From: Mark Brown
Date: Mon May 25 2020 - 07:31:14 EST

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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