On 08-05-18 08:36, Peter Rosin wrote:
On 2018-05-01 13:42, Mike Looijmans wrote:
Instead of just hogging the reset GPIO into deactivated state, activate and
then de-activate the reset. This allows for better recovery if the CPU was
reset halfway through an I2C transaction for example.
I can't see any problems with this, and a reset at load time can certainly
be a benefit. Some questions below though...
Cheers,
Peter
Signed-off-by: Mike Looijmans <mike.looijmans@xxxxxxxx>
---
drivers/i2c/muxes/i2c-mux-pca954x.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
index 09bafd3..13e10d0 100644
--- a/drivers/i2c/muxes/i2c-mux-pca954x.c
+++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
@@ -36,6 +36,7 @@
*/
#include <linux/device.h>
+#include <linux/delay.h>
#include <linux/gpio/consumer.h>
#include <linux/i2c.h>
#include <linux/i2c-mux.h>
@@ -389,10 +390,17 @@ static int pca954x_probe(struct i2c_client *client,
i2c_set_clientdata(client, muxc);
data->client = client;
- /* Get the mux out of reset if a reset GPIO is specified. */
- gpio = devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_LOW);
+ /* Reset the mux if a reset GPIO is specified. */
+ gpio = devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_HIGH);
if (IS_ERR(gpio))
return PTR_ERR(gpio);
+ if (gpio) {
+ /* Datasheet specifies a 4 ns reset-low time */
+ udelay(1);
ndelay(4) ?
I have several reasons for making it much much longer:
- A true 4ns pulse might not make it through the GPIO controller (on some
chips, the GPIO controller runs at 1/10th of the CPU speed or even less)
- Board designers tend to treat RESET signals as "DC", so a 250MHz pulse might
not make it through. There may be level converters and open-drain drives in
the signal path as well.
- I've only looked it op on a few chips, others may have different values
I think best is to just remove the comment line, it doesn't really help.
+ gpiod_set_value_cansleep(gpio, 0);
+ /* Datasheet specifies a 500 ns reset recovery time */
+ udelay(1);
ndelay(500) ?
Similar reasons as above.
+ }
match = of_match_device(of_match_ptr(pca954x_of_match), &client->dev);
if (match)
Kind regards,
Mike Looijmans
System Expert
TOPIC Products
Materiaalweg 4, NL-5681 RJ Best
Postbus 440, NL-5680 AK Best
Telefoon: +31 (0) 499 33 69 79
E-mail: mike.looijmans@xxxxxxxxxxxxxxxxx
Website: www.topicproducts.com
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