From: Andrew Jeffery <andrew@xxxxxxxx>
[ Upstream commit 7aeb353802611a8e655e019f09a370ff682af1a6 ]
Commit 6726fbff19bf ("pinctrl: aspeed: Fix GPI only function problem.")
fixes access to GPIO banks T and U on the AST2600. Both banks contain
input-only pins and the GPIO pin function is named GPITx and GPIUx
respectively. Unfortunately the fix had a negative impact on GPIO banks
D and E for the AST2400 and AST2500 where the GPIO pass-through
functions take similar "GPI"-style names. The net effect on the older
SoCs was that when the GPIO subsystem requested a pin in banks D or E be
muxed for GPIO, they were instead muxed for pass-through mode.
Mistakenly muxing pass-through mode e.g. breaks booting the host on
IBM's Witherspoon (AC922) platform where GPIOE0 is used for FSI.
Further exploit the names in the provided expression structure to
differentiate pass-through from pin-specific GPIO modes.
This follow-up fix gives the expected behaviour for the following tests:
Witherspoon BMC (AST2500):
1. Power-on the Witherspoon host
2. Request GPIOD1 be muxed via /sys/class/gpio/export
3. Request GPIOE1 be muxed via /sys/class/gpio/export
4. Request the balls for GPIOs E2 and E3 be muxed as GPIO pass-through
("GPIE2" mode) via a pinctrl hog in the devicetree
Rainier BMC (AST2600):
5. Request GPIT0 be muxed via /sys/class/gpio/export
6. Request GPIU0 be muxed via /sys/class/gpio/export
Together the tests demonstrate that all three pieces of functionality
(general GPIOs via 1, 2 and 3, input-only GPIOs via 5 and 6, pass-through
mode via 4) operate as desired across old and new SoCs.
Fixes: 9b92f5c51e9a ("pinctrl: aspeed: Fix GPI only function problem.")
Signed-off-by: Andrew Jeffery <andrew@xxxxxxxx>
Tested-by: Joel Stanley <joel@xxxxxxxxx>
Reviewed-by: Joel Stanley <joel@xxxxxxxxx>
Cc: Billy Tsai <billy_tsai@xxxxxxxxxxxxxx>
Cc: Joel Stanley <joel@xxxxxxxxx>
Link: https://lore.kernel.org/r/20201126063337.489927-1-andrew@xxxxxxxx
Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
drivers/pinctrl/aspeed/pinctrl-aspeed.c | 74 +++++++++++++++++++++++--
drivers/pinctrl/aspeed/pinmux-aspeed.h | 7 ++-
2 files changed, 72 insertions(+), 9 deletions(-)
diff --git a/drivers/pinctrl/aspeed/pinctrl-aspeed.c b/drivers/pinctrl/aspeed/pinctrl-aspeed.c
index 93b5654ff2828..22aca6d182c0c 100644
--- a/drivers/pinctrl/aspeed/pinctrl-aspeed.c
+++ b/drivers/pinctrl/aspeed/pinctrl-aspeed.c
@@ -277,14 +277,76 @@ int aspeed_pinmux_set_mux(struct pinctrl_dev *pctldev, unsigned int function,
static bool aspeed_expr_is_gpio(const struct aspeed_sig_expr *expr)
{
/*
- * The signal type is GPIO if the signal name has "GPI" as a prefix.
- * strncmp (rather than strcmp) is used to implement the prefix
- * requirement.
+ * We need to differentiate between GPIO and non-GPIO signals to
+ * implement the gpio_request_enable() interface. For better or worse
+ * the ASPEED pinctrl driver uses the expression names to determine
+ * whether an expression will mux a pin for GPIO.
*
- * expr->signal might look like "GPIOB1" in the GPIO case.
- * expr->signal might look like "GPIT0" in the GPI case.
+ * Generally we have the following - A GPIO such as B1 has:
+ *
+ * - expr->signal set to "GPIOB1"
+ * - expr->function set to "GPIOB1"
+ *
+ * Using this fact we can determine whether the provided expression is
+ * a GPIO expression by testing the signal name for the string prefix
+ * "GPIO".
+ *
+ * However, some GPIOs are input-only, and the ASPEED datasheets name
+ * them differently. An input-only GPIO such as T0 has:
+ *
+ * - expr->signal set to "GPIT0"
+ * - expr->function set to "GPIT0"
+ *
+ * It's tempting to generalise the prefix test from "GPIO" to "GPI" to
+ * account for both GPIOs and GPIs, but in doing so we run aground on
+ * another feature:
+ *
+ * Some pins in the ASPEED BMC SoCs have a "pass-through" GPIO
+ * function where the input state of one pin is replicated as the
+ * output state of another (as if they were shorted together - a mux
+ * configuration that is typically enabled by hardware strapping).
+ * This feature allows the BMC to pass e.g. power button state through
+ * to the host while the BMC is yet to boot, but take control of the
+ * button state once the BMC has booted by muxing each pin as a
+ * separate, pin-specific GPIO.
+ *
+ * Conceptually this pass-through mode is a form of GPIO and is named
+ * as such in the datasheets, e.g. "GPID0". This naming similarity
+ * trips us up with the simple GPI-prefixed-signal-name scheme
+ * discussed above, as the pass-through configuration is not what we
+ * want when muxing a pin as GPIO for the GPIO subsystem.
+ *
+ * On e.g. the AST2400, a pass-through function "GPID0" is grouped on
+ * balls A18 and D16, where we have:
+ *
+ * For ball A18:
+ * - expr->signal set to "GPID0IN"
+ * - expr->function set to "GPID0"
+ *
+ * For ball D16:
+ * - expr->signal set to "GPID0OUT"
+ * - expr->function set to "GPID0"
+ *
+ * By contrast, the pin-specific GPIO expressions for the same pins are
+ * as follows:
+ *
+ * For ball A18:
+ * - expr->signal looks like "GPIOD0"
+ * - expr->function looks like "GPIOD0"
+ *
+ * For ball D16:
+ * - expr->signal looks like "GPIOD1"
+ * - expr->function looks like "GPIOD1"
+ *
+ * Testing both the signal _and_ function names gives us the means
+ * differentiate the pass-through GPIO pinmux configuration from the
+ * pin-specific configuration that the GPIO subsystem is after: An
+ * expression is a pin-specific (non-pass-through) GPIO configuration
+ * if the signal prefix is "GPI" and the signal name matches the
+ * function name.
*/
- return strncmp(expr->signal, "GPI", 3) == 0;
+ return !strncmp(expr->signal, "GPI", 3) &&
+ !strcmp(expr->signal, expr->function);
}
static bool aspeed_gpio_in_exprs(const struct aspeed_sig_expr **exprs)
diff --git a/drivers/pinctrl/aspeed/pinmux-aspeed.h b/drivers/pinctrl/aspeed/pinmux-aspeed.h
index 140c5ce9fbc11..0aaa20653536f 100644
--- a/drivers/pinctrl/aspeed/pinmux-aspeed.h
+++ b/drivers/pinctrl/aspeed/pinmux-aspeed.h
@@ -452,10 +452,11 @@ struct aspeed_sig_desc {
* evaluation of the descriptors.
*
* @signal: The signal name for the priority level on the pin. If the signal
- * type is GPIO, then the signal name must begin with the string
- * "GPIO", e.g. GPIOA0, GPIOT4 etc.
+ * type is GPIO, then the signal name must begin with the
+ * prefix "GPI", e.g. GPIOA0, GPIT0 etc.
* @function: The name of the function the signal participates in for the
- * associated expression
+ * associated expression. For pin-specific GPIO, the function
+ * name must match the signal name.
* @ndescs: The number of signal descriptors in the expression
* @descs: Pointer to an array of signal descriptors that comprise the
* function expression
--
2.27.0
