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| author | Linus Walleij <linus.walleij@linaro.org> | 2012-05-22 11:46:45 +0200 |
|---|---|---|
| committer | Linus Walleij <linus.walleij@linaro.org> | 2012-06-17 19:44:44 +0200 |
| commit | daf731748f978efb4f741d19b499236e03bf667f (patch) | |
| tree | 4f6a27525562ee0717d628353de75f0ebb8ed917 /drivers/pinctrl/pinctrl-nomadik.c | |
| parent | pinctrl: mxs: Use kfree to fix build error (diff) | |
| download | linux-daf731748f978efb4f741d19b499236e03bf667f.tar.xz 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.c | 22 |
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) { |