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authorLinus Walleij <linus.walleij@linaro.org>2012-05-22 11:46:45 +0200
committerLinus Walleij <linus.walleij@linaro.org>2012-06-17 19:44:44 +0200
commitdaf731748f978efb4f741d19b499236e03bf667f (patch)
tree4f6a27525562ee0717d628353de75f0ebb8ed917 /drivers/pinctrl/pinctrl-nomadik.c
parent14e1e9f5cadb7cff3a2846c27cc1b9c8f207ee18 (diff)
downloadblackbird-op-linux-daf731748f978efb4f741d19b499236e03bf667f.tar.gz
blackbird-op-linux-daf731748f978efb4f741d19b499236e03bf667f.zip
pinctrl/nomadik: document Alt-C glitch
This documentation comment existed in an earlier patch set for GPIO consolidation, so I'm saving it for maintainability of the code. Acked-by: Stephen Warren <swarren@wwwdotorg.org> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Diffstat (limited to 'drivers/pinctrl/pinctrl-nomadik.c')
-rw-r--r--drivers/pinctrl/pinctrl-nomadik.c22
1 files changed, 21 insertions, 1 deletions
diff --git a/drivers/pinctrl/pinctrl-nomadik.c b/drivers/pinctrl/pinctrl-nomadik.c
index e8937e7e4999..3e7e47d6b385 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) {
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