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Commit daf73174 authored by Linus Walleij's avatar Linus Walleij
Browse files

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: default avatarStephen Warren <swarren@wwwdotorg.org>
Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
parent 14e1e9f5

drivers/pinctrl/pinctrl-nomadik.c

+21 −1
Original line number Diff line number Diff line
@@ -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) {