pinctrl: aspeed: Fix GPIO requests on pass-through banks

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@aj.id.au>
Tested-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Cc: Billy Tsai <billy_tsai@aspeedtech.com>
Cc: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20201126063337.489927-1-andrew@aj.id.au
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/drivers/pinctrl/aspeed/pinmux-aspeed.h b/drivers/pinctrl/aspeed/pinmux-aspeed.h
index f86739e800c3..dba5875ff276 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