Re: [PATCH v2 4/5] spi: axi-spi-engine: move message compile to optimize_message

[Jonathan Cameron <jic23@xxxxxxxxxx>]

On Mon, 19 Feb 2024 16:33:21 -0600
David Lechner <dlechner@xxxxxxxxxxxx> wrote:

> In the AXI SPI Engine driver, compiling the message is an expensive
> operation. Previously, it was done per message transfer in the
> prepare_message hook. This patch moves the message compile to the
> optimize_message hook so that it is only done once per message in
> cases where the peripheral driver calls spi_optimize_message().
> 
> This can be a significant performance improvement for some peripherals.
> For example, the ad7380 driver saw a 13% improvement in throughput
> when using the AXI SPI Engine driver with this patch.
> 
> Since we now need two message states, one for the optimization stage
> that doesn't change for the lifetime of the message and one that is
> reset on each transfer for managing the current transfer state, the old
> msg->state is split into msg->opt_state and spi_engine->msg_state. The
> latter is included in the driver struct now since there is only one
> current message at a time that can ever use it and it is in a hot path
> so avoiding allocating a new one on each message transfer saves a few
> cpu cycles and lets us get rid of the prepare_message callback.
> 
> Signed-off-by: David Lechner <dlechner@xxxxxxxxxxxx>
Whilst I'm not familiar with this driver, from a quick look at this
patch and the driver code, looks fine to me. So FWIW
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>