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spi: bcm2835aux: make the polling duration limits configurable

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Under some circumstances the default 30 us polling limit is not optimal
and may lead to long delays because we are waiting on an interrupt.
with this patch we have the possibility to influence this policy.

So make this limit (in us) configurable via a module parameters
(but also modifyable via /sys/modules/...)

Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Martin Sperl 2019-03-30 09:31:06 +00:00 committed by Mark Brown
parent ccd978b708
commit 5fd917afc4
No known key found for this signature in database
GPG Key ID: 24D68B725D5487D0
1 changed files with 14 additions and 11 deletions
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25
drivers/spi/spi-bcm2835aux.c
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@ -36,6 +36,12 @@
#include <linux/spi/spi.h>
#include <linux/spinlock.h>
/* define polling limits */
unsigned int polling_limit_us = 30;
module_param(polling_limit_us, uint, 0664);
MODULE_PARM_DESC(polling_limit_us,
"time in us to run a transfer in polling mode - if zero no polling is used\n");
/*
* spi register defines
*
@ -88,10 +94,6 @@
#define BCM2835_AUX_SPI_STAT_BUSY 0x00000040
#define BCM2835_AUX_SPI_STAT_BITCOUNT 0x0000003F
/* timeout values */
#define BCM2835_AUX_SPI_POLLING_LIMIT_US 30
#define BCM2835_AUX_SPI_POLLING_JIFFIES 2
struct bcm2835aux_spi {
void __iomem *regs;
struct clk *clk;
@ -269,8 +271,8 @@ static int bcm2835aux_spi_transfer_one_poll(struct spi_master *master,
bcm2835aux_wr(bs, BCM2835_AUX_SPI_CNTL1, bs->cntl[1]);
bcm2835aux_wr(bs, BCM2835_AUX_SPI_CNTL0, bs->cntl[0]);
/* set the timeout */
timeout = jiffies + BCM2835_AUX_SPI_POLLING_JIFFIES;
/* set the timeout to at least 2 jiffies */
timeout = jiffies + 2 + HZ * polling_limit_us / 1000000;
/* loop until finished the transfer */
while (bs->rx_len) {
@ -299,8 +301,8 @@ static int bcm2835aux_spi_transfer_one(struct spi_master *master,
struct spi_transfer *tfr)
{
struct bcm2835aux_spi *bs = spi_master_get_devdata(master);
unsigned long spi_hz, clk_hz, speed;
unsigned long spi_used_hz;
unsigned long spi_hz, clk_hz, speed, spi_used_hz;
unsigned long hz_per_byte, byte_limit;
/* calculate the registers to handle
*
@ -344,14 +346,15 @@ static int bcm2835aux_spi_transfer_one(struct spi_master *master,
* of Hz per byte per polling limit. E.g., we can transfer 1 byte in
* 30 µs per 300,000 Hz of bus clock.
*/
#define HZ_PER_BYTE ((9 * 1000000) / BCM2835_AUX_SPI_POLLING_LIMIT_US)
hz_per_byte = polling_limit_us ? (9 * 1000000) / polling_limit_us : 0;
byte_limit = hz_per_byte ? spi_used_hz / hz_per_byte : 1;
/* run in polling mode for short transfers */
if (tfr->len < spi_used_hz / HZ_PER_BYTE)
if (tfr->len < byte_limit)
return bcm2835aux_spi_transfer_one_poll(master, spi, tfr);
/* run in interrupt mode for all others */
return bcm2835aux_spi_transfer_one_irq(master, spi, tfr);
#undef HZ_PER_BYTE
}
static int bcm2835aux_spi_prepare_message(struct spi_master *master,