[PATCH v2 2/2] mfd: axp20x: Fix AXP806 access errors on cold boot

[Lee Jones]

Mark,

Is the following valid/necessary?

On Wed, 23 Nov 2016, Chen-Yu Tsai wrote:
> The AXP806 supports either master/standalone or slave mode.
> Slave mode allows sharing the serial bus, even with multiple
> AXP806 which all have the same hardware address.
> 
> This is done with extra "serial interface address extension",
> or AXP806_BUS_ADDR_EXT, and "register address extension", or
> AXP806_REG_ADDR_EXT, registers. The former is read-only, with
> 1 bit customizable at the factory, and 1 bit depending on the
> state of an external pin. The latter is writable. Only when
> the these device addressing bits (in the upper 4 bits of the
> registers) match, will the device respond to operations on
> its other registers.
> 
> The AXP806_REG_ADDR_EXT was previously configured by Allwinner's
> bootloader. Work on U-boot SPL support now allows us to switch
> to mainline U-boot, which doesn't do this for us. There might
> be other bare minimum bootloaders out there which don't to this
> either. It's best to handle this in the kernel.
> 
> This patch sets AXP806_REG_ADDR_EXT to 0x10, which is what we
> know to be the proper value for a standard AXP806 in slave mode.
> Afterwards it will reinitialize the regmap cache, to purge any
> invalid stale values.
> 
> Signed-off-by: Chen-Yu Tsai <wens at csie.org>
> ---
>  drivers/mfd/axp20x.c | 38 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/drivers/mfd/axp20x.c b/drivers/mfd/axp20x.c
> index cdaeb34a9a38..a0166c667656 100644
> --- a/drivers/mfd/axp20x.c
> +++ b/drivers/mfd/axp20x.c
> @@ -31,6 +31,8 @@
>  
>  #define AXP20X_OFF	0x80
>  
> +#define AXP806_REG_ADDR_EXT_ADDR_SLAVE_MODE	BIT(4)
> +
>  static const char * const axp20x_model_names[] = {
>  	"AXP152",
>  	"AXP202",
> @@ -829,6 +831,42 @@ int axp20x_device_probe(struct axp20x_dev *axp20x)
>  {
>  	int ret;
>  
> +	/*
> +	 * The AXP806 supports either master/standalone or slave mode.
> +	 * Slave mode allows sharing the serial bus, even with multiple
> +	 * AXP806 which all have the same hardware address.
> +	 *
> +	 * This is done with extra "serial interface address extension",
> +	 * or AXP806_BUS_ADDR_EXT, and "register address extension", or
> +	 * AXP806_REG_ADDR_EXT, registers. The former is read-only, with
> +	 * 1 bit customizable at the factory, and 1 bit depending on the
> +	 * state of an external pin. The latter is writable. Only when
> +	 * the these device addressing bits (in the upper 4 bits of the
> +	 * registers) match, will the device respond to operations on its
> +	 * other registers.
> +	 *
> +	 * Since we only support an AXP806 chained to an AXP809 in slave
> +	 * mode, and there isn't any existing hardware which uses AXP806
> +	 * in master mode, or has 2 AXP806s in the same system, we can
> +	 * just program the register address extension to the slave mode
> +	 * address.
> +	 */
> +	if (axp20x->variant == AXP806_ID) {
> +		/* Write to the register address extension register */
> +		regmap_write(axp20x->regmap, AXP806_REG_ADDR_EXT,
> +			     AXP806_REG_ADDR_EXT_ADDR_SLAVE_MODE);
> +
> +		/* Make sure the write hits the device */
> +		regcache_sync_region(axp20x->regmap, AXP806_REG_ADDR_EXT,
> +				     AXP806_REG_ADDR_EXT);
> +
> +		/*
> +		 * Reinitialize the regmap cache in case the device didn't
> +		 * properly respond to our reads before.
> +		 */
> +		regmap_reinit_cache(axp20x->regmap, axp20x->regmap_cfg);
> +	}
> +
>  	ret = regmap_add_irq_chip(axp20x->regmap, axp20x->irq,
>  				  IRQF_ONESHOT | IRQF_SHARED, -1,
>  				  axp20x->regmap_irq_chip,

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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