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>
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@ -1438,7 +1438,27 @@ static int nmk_pmx_enable(struct pinctrl_dev *pctldev, unsigned function,
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dev_dbg(npct->dev, "enable group %s, %u pins\n", g->name, g->npins);
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/* Handle this special glitch on altfunction C */
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/*
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* If we're setting altfunc C by setting both AFSLA and AFSLB to 1,
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* we may pass through an undesired state. In this case we take
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* some extra care.
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*
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* Safe sequence used to switch IOs between GPIO and Alternate-C mode:
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* - Save SLPM registers (since we have a shadow register in the
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* nmk_chip we're using that as backup)
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* - Set SLPM=0 for the IOs you want to switch and others to 1
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* - Configure the GPIO registers for the IOs that are being switched
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* - Set IOFORCE=1
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* - Modify the AFLSA/B registers for the IOs that are being switched
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* - Set IOFORCE=0
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* - Restore SLPM registers
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* - Any spurious wake up event during switch sequence to be ignored
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* and cleared
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*
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* We REALLY need to save ALL slpm registers, because the external
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* IOFORCE will switch *all* ports to their sleepmode setting to as
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* to avoid glitches. (Not just one port!)
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*/
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glitch = (g->altsetting == NMK_GPIO_ALT_C);
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if (glitch) {
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