On 21/02/2018 02:04, Jan Kundrát wrote:
Apart from the usual stuff, the debugfs code is currently also used for
one non-obvious side effect. It attempts to check whether the chip's
registers are still set to an expected value, and if not, re-initializes
them. It seems that the driver has "always" done so.
The code, however, also checks the INTF register which normally
indicates which pins have caused the recent interrupt. That's a volatile
register, and the datasheet says that writes are ignored in there.
When I'm just cat-ing /sys/kernel/debug/gpio with no SPI traffic and no
nosie on the GPIO lines, I'm not getting any warnings. Once I actually
use these GPIOs and cat that file in parallel, I always seem to get a:
mcp23s08 spi1.1: restoring reg 0x07 from 0x0000 to 0xffff (power-loss?)
This might be a sign that I should not leave my unused inputs floating,
but the code should not be checking a volatile register, anyway. Let's
simply skip this last item in the iteration. I was also considering
removing this enitre re-initialization because it's non-obvious, but the
code survived various refactorings already and has sign-offs by people
who know more than I do, so let's leave it as-is. For now :).
Signed-off-by: Jan Kundrát <jan.kundrat@xxxxxxxxx>
---
drivers/pinctrl/pinctrl-mcp23s08.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/pinctrl/pinctrl-mcp23s08.c b/drivers/pinctrl/pinctrl-mcp23s08.c
index fd9d27e8126e..bbef9833edb8 100644
--- a/drivers/pinctrl/pinctrl-mcp23s08.c
+++ b/drivers/pinctrl/pinctrl-mcp23s08.c
@@ -664,7 +664,7 @@ static int mcp23s08_irq_setup(struct mcp23s08 *mcp)
* can be used to fix state for MCP23xxx, that temporary
* lost its power supply.
*/
-#define MCP23S08_CONFIG_REGS 8
+#define MCP23S08_CONFIG_REGS 7
static int __check_mcp23s08_reg_cache(struct mcp23s08 *mcp)
{
int cached[MCP23S08_CONFIG_REGS];
I agree INTF shouldn't be part of this loop.
I also agree that the entire function is non-obvious.
Comparing the in-chip values to the cached values seems reasonable for debugging
But rewriting them doesn't.
Reviewed-by: Phil Reid <preid@xxxxxxxxxxxxxxxxx>
--
Regards
Phil
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