From 7547b5969e069520d4cf23ba43b4ac889f8bd0ef Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Jan=20Kundr=C3=A1t?= Date: Tue, 20 Feb 2018 19:04:47 +0100 Subject: [PATCH] pinctrl: mcp23s08: debugfs: Do not restore the INTF register MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Phil Reid Signed-off-by: Linus Walleij --- 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 022307dd4b54..4a8a8efadefa 100644 --- a/drivers/pinctrl/pinctrl-mcp23s08.c +++ b/drivers/pinctrl/pinctrl-mcp23s08.c @@ -666,7 +666,7 @@ 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];