linux-kernel - Re: [PATCH 2/5] regulator: st-flashss: Add a regulator driver for flashss vsense.

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Date:	Wed, 13 Apr 2016 09:59:00 +0200
From:	Giuseppe CAVALLARO <peppe.cavallaro@...com>
To:	Mark Brown <broonie@...nel.org>,
	Peter Griffin <peter.griffin@...aro.org>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <lgirdwood@...il.com>,
	<srinivas.kandagatla@...il.com>, <maxime.coquelin@...com>,
	<patrice.chotard@...com>, <lee.jones@...aro.org>,
	<devicetree@...r.kernel.org>, Youssef TRIKI <youssef.triki@...com>
Subject: Re: [PATCH 2/5] regulator: st-flashss: Add a regulator driver for
 flashss vsense.

On 4/13/2016 8:15 AM, Mark Brown wrote:
>> >+static void st_get_satinize_powerup_voltage(struct st_vsense *vsense)
>> >+{
>> >+	void __iomem *ioaddr = vsense->ioaddr;
>> >+	u32 value = readl_relaxed(ioaddr);
>> >+
>> >+	dev_dbg(vsense->dev, "Initial start-up value: (0x%08x)\n", value);
>> >+
>> >+	/* Sanitize voltage values forcing what is provided from start-up */
>> >+	if (value & TOP_VSENSE_CONFIG_LATCHED_PSW_EMMC)
>> >+		value |= TOP_VSENSE_CONFIG_REG_PSW_EMMC;
>> >+	else
>> >+		value &= ~TOP_VSENSE_CONFIG_REG_PSW_EMMC;
>> >+
>> >+	if (value & TOP_VSENSE_CONFIG_LATCHED_PSW_NAND)
>> >+		value |= TOP_VSENSE_CONFIG_REG_PSW_NAND;
>> >+	else
>> >+		value &= ~TOP_VSENSE_CONFIG_REG_PSW_NAND;
>> >+
>> >+	if (value & TOP_VSENSE_CONFIG_LATCHED_PSW_SPI)
>> >+		value |= TOP_VSENSE_CONFIG_REG_PSW_SPI;
>> >+	else
>> >+		value &= ~TOP_VSENSE_CONFIG_REG_PSW_SPI;
> This looks like a very complicated way of writing
>
> 	value &= TOP_VSENSE_CONFIG_LATCHED_PSW_SPI |
> 		TOP_VSENSE_CONFIG_LATCHED_PSW_NAND |
> 		TOP_VSENSE_CONFIG_REG_PSW_EMMC
>
> or am I missing something?  Why do we need to do this anyway, it's very
> surprsing?
>

This functions is to sanitize the vsense voltages when the regulator
is probed and in some circumstances the reset value of this register
does not reflect the hw status/config. For example, by default, after
the reset, the bit 0 is set so the EMMC, inside the flash subsystem,
is supposed to operate at 3v3. But the latched bit 24 can be 0 on
a platform where it is actually set at 1v8.
So the bit 0 must be reset to keep this coherent and to allow MMC
framework to properly setup the Vdd when the framework starts.

Hoping this can help.

Regards
peppe