From: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
To: Mark Brown <broonie@kernel.org>,
"linux-spi@vger.kernel.org" <linux-spi@vger.kernel.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Fabio Estevam <festevam@gmail.com>,
Rasmus Villemoes <Rasmus.Villemoes@prevas.se>
Subject: [RFC PATCH 4/4] spi: spi-fsl-spi: automatically adapt bits-per-word in cpu mode
Date: Wed, 27 Mar 2019 14:30:52 +0000 [thread overview]
Message-ID: <20190327143040.16013-5-rasmus.villemoes@prevas.dk> (raw)
In-Reply-To: <20190327143040.16013-1-rasmus.villemoes@prevas.dk>
Taking one interrupt for every byte is rather slow. Since the
controller is perfectly capable of transmitting 32 bits at a time,
change t->bits_per-word to 32 when the length is divisible by 4 and
large enough that the reduced number of interrupts easily compensates
for the one or two extra fsl_spi_setup_transfer() calls this causes.
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
---
drivers/spi/spi-fsl-spi.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/drivers/spi/spi-fsl-spi.c b/drivers/spi/spi-fsl-spi.c
index e2b341943796..b36ac6aa3b1f 100644
--- a/drivers/spi/spi-fsl-spi.c
+++ b/drivers/spi/spi-fsl-spi.c
@@ -363,12 +363,28 @@ static int fsl_spi_bufs(struct spi_device *spi, struct spi_transfer *t,
static int fsl_spi_do_one_msg(struct spi_master *master,
struct spi_message *m)
{
+ struct mpc8xxx_spi *mpc8xxx_spi = spi_master_get_devdata(master);
struct spi_device *spi = m->spi;
struct spi_transfer *t, *first;
unsigned int cs_change;
const int nsecs = 50;
int status, last_bpw;
+ /*
+ * In CPU mode, optimize large byte transfers to use larger
+ * bits_per_word values to reduce number of interrupts taken.
+ */
+ if (!(mpc8xxx_spi->flags & SPI_CPM_MODE)) {
+ list_for_each_entry(t, &m->transfers, transfer_list) {
+ if (t->len < 256 || t->bits_per_word != 8)
+ continue;
+ if ((t->len & 3) == 0)
+ t->bits_per_word = 32;
+ else if ((t->len & 1) == 0)
+ t->bits_per_word = 16;
+ }
+ }
+
/* Don't allow changes if CS is active */
cs_change = 1;
list_for_each_entry(t, &m->transfers, transfer_list) {
--
2.20.1
next prev parent reply other threads:[~2019-03-27 14:31 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-27 14:30 [RFC PATCH 0/4] spi: spi-fsl-spi: try to make cpu-mode transfers faster Rasmus Villemoes
2019-03-27 14:30 ` [RFC PATCH 1/4] spi: spi-fsl-spi: remove always-true conditional in fsl_spi_do_one_msg Rasmus Villemoes
2019-04-01 8:54 ` Applied "spi: spi-fsl-spi: remove always-true conditional in fsl_spi_do_one_msg" to the spi tree Mark Brown
2019-03-27 14:30 ` [RFC PATCH 2/4] spi: spi-fsl-spi: relax message sanity checking a little Rasmus Villemoes
2019-04-01 8:54 ` Applied "spi: spi-fsl-spi: relax message sanity checking a little" to the spi tree Mark Brown
2019-03-27 14:30 ` [RFC PATCH 3/4] spi: spi-fsl-spi: allow changing bits_per_word while CS is still active Rasmus Villemoes
2019-03-27 14:30 ` Rasmus Villemoes [this message]
2019-04-01 7:34 ` [RFC PATCH 0/4] spi: spi-fsl-spi: try to make cpu-mode transfers faster Mark Brown
2019-04-02 8:43 ` Rasmus Villemoes
2019-04-02 9:10 ` Mark Brown
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