Re: [PATCH 1/2] spi: axi-spi-engine: remove use of ida for sync id

["Nuno Sá" <noname.nuno@gmail.com>]

On Tue, 2024-02-06 at 14:31 -0600, David Lechner wrote:
> Profiling has shown that ida_alloc_range() accounts for about 10% of the
> time spent in spi_sync() when using the AXI SPI Engine controller. This
> call is used to create a unique id for each SPI message to match to an
> IRQ when the message is complete.
> 
> Since the core SPI code serializes messages in a message queue, we can
> only have one message in flight at a time, namely host->cur_msg. This
> means that we can use a fixed value instead of a unique id for each
> message since there can never be more than one message pending at a
> time.
> 
> This patch removes the use of ida for the sync id and replaces it with a
> constant value. This simplifies the driver and improves performance.
> 
> Signed-off-by: David Lechner <dlechner@baylibre.com>
> ---

With the removed header:

Reviewed-by: Nuno Sa <nuno.sa@analog.com>

(Christophe suggestion is also pretty good but I would likely do it in a
different patch - maybe we could even annotate the flex array with __counted_by)

- Nuno Sá

>  drivers/spi/spi-axi-spi-engine.c | 27 ++++++---------------------
>  1 file changed, 6 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/spi/spi-axi-spi-engine.c b/drivers/spi/spi-axi-spi-
> engine.c
> index 6b0c72bf3395..9cc602075c17 100644
> --- a/drivers/spi/spi-axi-spi-engine.c
> +++ b/drivers/spi/spi-axi-spi-engine.c
> @@ -57,6 +57,9 @@
>  #define SPI_ENGINE_TRANSFER_WRITE		0x1
>  #define SPI_ENGINE_TRANSFER_READ		0x2
>  
> +/* Arbitrary sync ID for use by host->cur_msg */
> +#define AXI_SPI_ENGINE_CUR_MSG_SYNC_ID		0x1
> +
>  #define SPI_ENGINE_CMD(inst, arg1, arg2) \
>  	(((inst) << 12) | ((arg1) << 8) | (arg2))
>  
> @@ -98,8 +101,6 @@ struct spi_engine_message_state {
>  	unsigned int rx_length;
>  	/** @rx_buf: Bytes not yet written to the RX FIFO. */
>  	uint8_t *rx_buf;
> -	/** @sync_id: ID to correlate SYNC interrupts with this message. */
> -	u8 sync_id;
>  };
>  
>  struct spi_engine {
> @@ -109,7 +110,6 @@ struct spi_engine {
>  	spinlock_t lock;
>  
>  	void __iomem *base;
> -	struct ida sync_ida;
>  	struct timer_list watchdog_timer;
>  	struct spi_controller *controller;
>  
> @@ -483,9 +483,7 @@ static irqreturn_t spi_engine_irq(int irq, void *devid)
>  	}
>  
>  	if (pending & SPI_ENGINE_INT_SYNC && msg) {
> -		struct spi_engine_message_state *st = msg->state;
> -
> -		if (completed_id == st->sync_id) {
> +		if (completed_id == AXI_SPI_ENGINE_CUR_MSG_SYNC_ID) {
>  			if (timer_delete_sync(&spi_engine->watchdog_timer)) {
>  				msg->status = 0;
>  				msg->actual_length = msg->frame_length;
> @@ -510,10 +508,8 @@ static int spi_engine_prepare_message(struct
> spi_controller *host,
>  				      struct spi_message *msg)
>  {
>  	struct spi_engine_program p_dry, *p;
> -	struct spi_engine *spi_engine = spi_controller_get_devdata(host);
>  	struct spi_engine_message_state *st;
>  	size_t size;
> -	int ret;
>  
>  	st = kzalloc(sizeof(*st), GFP_KERNEL);
>  	if (!st)
> @@ -531,18 +527,10 @@ static int spi_engine_prepare_message(struct
> spi_controller *host,
>  		return -ENOMEM;
>  	}
>  
> -	ret = ida_alloc_range(&spi_engine->sync_ida, 0, U8_MAX, GFP_KERNEL);
> -	if (ret < 0) {
> -		kfree(p);
> -		kfree(st);
> -		return ret;
> -	}
> -
> -	st->sync_id = ret;
> -
>  	spi_engine_compile_message(msg, false, p);
>  
> -	spi_engine_program_add_cmd(p, false, SPI_ENGINE_CMD_SYNC(st-
> >sync_id));
> +	spi_engine_program_add_cmd(p, false, SPI_ENGINE_CMD_SYNC(
> +						AXI_SPI_ENGINE_CUR_MSG_SYNC_I
> D));
>  
>  	st->p = p;
>  	st->cmd_buf = p->instructions;
> @@ -555,10 +543,8 @@ static int spi_engine_prepare_message(struct
> spi_controller *host,
>  static int spi_engine_unprepare_message(struct spi_controller *host,
>  					struct spi_message *msg)
>  {
> -	struct spi_engine *spi_engine = spi_controller_get_devdata(host);
>  	struct spi_engine_message_state *st = msg->state;
>  
> -	ida_free(&spi_engine->sync_ida, st->sync_id);
>  	kfree(st->p);
>  	kfree(st);
>  
> @@ -640,7 +626,6 @@ static int spi_engine_probe(struct platform_device *pdev)
>  	spi_engine = spi_controller_get_devdata(host);
>  
>  	spin_lock_init(&spi_engine->lock);
> -	ida_init(&spi_engine->sync_ida);
>  	timer_setup(&spi_engine->watchdog_timer, spi_engine_timeout,
> TIMER_IRQSAFE);
>  	spi_engine->controller = host;
>  
>