patches.renesas/0094-spi-rspi-Only-enable-interrupts-when-there-s-a-need-.patch

From 5e1ba70515975b8c87b7aa2bd4ae730f307780a8 Mon Sep 17 00:00:00 2001
From: Geert Uytterhoeven <geert+renesas@linux-m68k.org>
Date: Tue, 4 Feb 2014 11:06:24 +0100
Subject: spi: rspi: Only enable interrupts when there's a need to wait

rspi_wait_for_interrupt() unconditionally enables interrupts, even when the
wait condition is already satisfied. This causes a high interrupt load (2
interrupts/byte for full-duplex Single SPI transfers, 1 interrupt/byte for
RSPI with TX Only mode, or QSPI in unidirectional Dual or Quad Transfer
mode).

Change this to return immediately when the wait condition is satisfied.
This dramatically reduces the interrupt load, especially in high-speed
Quad Transfer mode, and increases transfer speed, as no interrupts need to
be handled when there's space available in the output FIFO, or data
available in the input FIFO.

Benchmark results for QSPI on r8a7791 while reading 1 MiB from 30 MHz SPI
FLASH on the Koelsch development board:

Before:
                        Single SPI      Dual SPI        Quad SPI
    Interrupts:         2096856         1048592         1048594
    Mbps:               0.9             1.6             1.6

After:

                        Single SPI      Dual SPI        Quad SPI
    Interrupts:         1048569         21295           8
    Mbps:               0.7             10.8            12.9

I don't know why Single SPI slowed down a bit.

I've also verified functionality for RSPI-RZ on r7s72100, but don't have
benchmark results as there's no SPI FLASH connected to RSPI on the Genmai
development board. Unlike RSPI and QSPI, RSPI-RZ has separate interrupts
for RX and TX, which shows that Single SPI transfers now generate (mostly)
RX interrupts, as expected.

Signed-off-by: Geert Uytterhoeven <geert+renesas@linux-m68k.org>
Signed-off-by: Mark Brown <broonie@linaro.org>
(cherry picked from commit 5dd1ad23af689591d70be06ee6efcc57d1ec2d16)
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
---
 drivers/spi/spi-rspi.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/spi/spi-rspi.c b/drivers/spi/spi-rspi.c
index e5cfc3d77b8c..04528888a53f 100644
--- a/drivers/spi/spi-rspi.c
+++ b/drivers/spi/spi-rspi.c
@@ -391,6 +391,9 @@ static int rspi_wait_for_interrupt(struct rspi_data *rspi, u8 wait_mask,
 	int ret;
 
 	rspi->spsr = rspi_read8(rspi, RSPI_SPSR);
+	if (rspi->spsr & wait_mask)
+		return 0;
+
 	rspi_enable_irq(rspi, enable_bit);
 	ret = wait_event_timeout(rspi->wait, rspi->spsr & wait_mask, HZ);
 	if (ret == 0 && !(rspi->spsr & wait_mask))
-- 
2.1.2