Patch "Subject:[For 4.19/4.14] spi: spi-fsl-spi: automatically adapt bits-per-word in cpu mode" has been added to the 4.14-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    Subject:[For 4.19/4.14] spi: spi-fsl-spi: automatically adapt bits-per-word in cpu mode

to the 4.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     spi-spi-fsl-spi-automatically-adapt-bits-per-word-in-cpu-mode.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From christophe.leroy@csgroup.eu Mon May 15 15:08:06 2023
From: Christophe Leroy <christophe.leroy@csgroup.eu>
Date: Mon, 15 May 2023 16:07:13 +0200
Subject:[For 4.19/4.14] spi: spi-fsl-spi: automatically adapt bits-per-word in cpu mode
To: gregkh@linuxfoundation.org, stable@vger.kernel.org
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Rasmus Villemoes <rasmus.villemoes@prevas.dk>, Mark Brown <broonie@kernel.org>
Message-ID: <674d9af640acf4aa04abd642cc81de926d3271ed.1684158520.git.christophe.leroy@csgroup.eu>

From: Rasmus Villemoes <rasmus.villemoes@prevas.dk>

(cherry picked from upstream af0e6242909c3c4297392ca3e94eff1b4db71a97)

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>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/spi/spi-fsl-spi.c |   16 ++++++++++++++++
 1 file changed, 16 insertions(+)

--- a/drivers/spi/spi-fsl-spi.c
+++ b/drivers/spi/spi-fsl-spi.c
@@ -357,12 +357,28 @@ static int fsl_spi_bufs(struct spi_devic
 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;
 
+	/*
+	 * 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 */
 	first = list_first_entry(&m->transfers, struct spi_transfer,
 			transfer_list);


Patches currently in stable-queue which might be from christophe.leroy@csgroup.eu are

queue-4.14/spi-fsl-cpm-use-16-bit-mode-for-large-transfers-with-even-size.patch
queue-4.14/spi-fsl-spi-re-organise-transfer-bits_per_word-adaptation.patch
queue-4.14/spi-spi-fsl-spi-automatically-adapt-bits-per-word-in-cpu-mode.patch