[PATCH] pinctrl/nomadik: document Alt-C glitch
From: Linus Walleij <hidden>
Date: 2012-06-15 12:07:36
From: Linus Walleij <redacted> This documentation comment existed in an earlier patch set for GPIO consolidation, so I'm saving it for maintainability of the code. Signed-off-by: Linus Walleij <redacted> --- drivers/pinctrl/pinctrl-nomadik.c | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-)
diff --git a/drivers/pinctrl/pinctrl-nomadik.c b/drivers/pinctrl/pinctrl-nomadik.c
index e8937e7..3e7e47d 100644
--- a/drivers/pinctrl/pinctrl-nomadik.c
+++ b/drivers/pinctrl/pinctrl-nomadik.c@@ -1438,7 +1438,27 @@ static int nmk_pmx_enable(struct pinctrl_dev *pctldev, unsigned function, dev_dbg(npct->dev, "enable group %s, %u pins\n", g->name, g->npins); - /* Handle this special glitch on altfunction C */ + /* + * If we're setting altfunc C by setting both AFSLA and AFSLB to 1, + * we may pass through an undesired state. In this case we take + * some extra care. + * + * Safe sequence used to switch IOs between GPIO and Alternate-C mode: + * - Save SLPM registers (since we have a shadow register in the + * nmk_chip we're using that as backup) + * - Set SLPM=0 for the IOs you want to switch and others to 1 + * - Configure the GPIO registers for the IOs that are being switched + * - Set IOFORCE=1 + * - Modify the AFLSA/B registers for the IOs that are being switched + * - Set IOFORCE=0 + * - Restore SLPM registers + * - Any spurious wake up event during switch sequence to be ignored + * and cleared + * + * We REALLY need to save ALL slpm registers, because the external + * IOFORCE will switch *all* ports to their sleepmode setting to as + * to avoid glitches. (Not just one port!) + */ glitch = (g->altsetting == NMK_GPIO_ALT_C); if (glitch) {
--
1.7.9.2