diff mbox series

[V2,9/9] spi: bcm2835aux: make the polling duration limits configurable

Message ID 20190324175002.28969-10-kernel@martin.sperl.org
State New
Headers show
Series spi: bcm2835aux: bug fixes and improvements | expand

Commit Message

Martin Sperl March 24, 2019, 5:50 p.m. UTC 
From: Martin Sperl <kernel@martin.sperl.org>

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>

---
Changelog:
  V1 -> V2: remove the dependency on a different patchset focused on
	    making cs_change delay configurable

---
 drivers/spi/spi-bcm2835aux.c | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

--
2.11.0

Comments

Stefan Wahren March 25, 2019, 9:44 a.m. UTC | #1 
Hi Martin,

Am 24.03.19 um 18:50 schrieb kernel@martin.sperl.org:
> From: Martin Sperl <kernel@martin.sperl.org>
>
> 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>
>
> ---
> Changelog:
>   V1 -> V2: remove the dependency on a different patchset focused on
> 	    making cs_change delay configurable
>
> ---
>  drivers/spi/spi-bcm2835aux.c | 25 ++++++++++++++-----------
>  1 file changed, 14 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/spi/spi-bcm2835aux.c b/drivers/spi/spi-bcm2835aux.c
> index d2b58060b333..df065108122b 100644
> --- a/drivers/spi/spi-bcm2835aux.c
> +++ b/drivers/spi/spi-bcm2835aux.c
> @@ -37,6 +37,12 @@
>  #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\n");
> +
could you please document the case polling_limit_us = 0 ?
Martin Sperl March 25, 2019, 9:49 a.m. UTC | #2 
> On 25.03.2019, at 10:44, Stefan Wahren <stefan.wahren@i2se.com> wrote:
> 
> Hi Martin,
> 
> Am 24.03.19 um 18:50 schrieb kernel@martin.sperl.org:
>> From: Martin Sperl <kernel@martin.sperl.org>
>> 
>> +/* 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\n");
>> +
> could you please document the case polling_limit_us = 0 ?

Means no polling under any circumstances - I can add it as a comment in V3.

martin
Stefan Wahren March 25, 2019, 9:59 a.m. UTC | #3 
Am 25.03.19 um 10:49 schrieb kernel@martin.sperl.org:
>> On 25.03.2019, at 10:44, Stefan Wahren <stefan.wahren@i2se.com> wrote:
>>
>> Hi Martin,
>>
>> Am 24.03.19 um 18:50 schrieb kernel@martin.sperl.org:
>>> From: Martin Sperl <kernel@martin.sperl.org>
>>>
>>> +/* 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\n");
>>> +
>> could you please document the case polling_limit_us = 0 ?
> Means no polling under any circumstances - I can add it as a comment in V3.
I meant the parameter description, because users shouldn't be forced to
look at the source code.
>
> martin
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
diff mbox series

Patch

diff --git a/drivers/spi/spi-bcm2835aux.c b/drivers/spi/spi-bcm2835aux.c
index d2b58060b333..df065108122b 100644
--- a/drivers/spi/spi-bcm2835aux.c
+++ b/drivers/spi/spi-bcm2835aux.c
@@ -37,6 +37,12 @@ 
 #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\n");
+
 /*
  * spi register defines
  *
@@ -89,10 +95,6 @@ 
 #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;
@@ -325,8 +327,8 @@  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) {
@@ -356,8 +358,8 @@  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
 	 *
@@ -401,14 +403,15 @@  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,