On Fri, 11 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 <w...@csie.org>
> ---
> drivers/mfd/axp20x.c | 35 +++++++++++++++++++++++++++++++++++
> 1 file changed, 35 insertions(+)
>
> diff --git a/drivers/mfd/axp20x.c b/drivers/mfd/axp20x.c
> index cdaeb34a9a38..2f5d46f28511 100644
> --- a/drivers/mfd/axp20x.c
> +++ b/drivers/mfd/axp20x.c
> @@ -829,6 +829,41 @@ 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, 0x10);
Please define 0x10.
> + /* 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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