Subject: Re: [RFC v5 net-next 02/13] mfd: ocelot: offer an interface for MFD children to get regmaps

From: Lee Jones <[email-masked]>
Date: Wed, 29 Dec 2021 15:23:59 +0000

On Sat, 18 Dec 2021, Colin Foster wrote:

> Child devices need to get a regmap from a resource struct, specifically
> from the MFD parent. The MFD parent has the interface to the hardware
> layer, which could be I2C, SPI, PCIe, etc.
> 
> This is somewhat a hack... ideally child devices would interface with the
> struct device* directly, by way of a function like
> devm_get_regmap_from_resource which would be akin to
> devm_get_and_ioremap_resource. A less ideal option would be to interface
> directly with MFD to get a regmap from the parent.
> 
> This solution is even less ideal than both of the two suggestions, so is
> intentionally left in a separate commit after the initial MFD addition.
> 
> Signed-off-by: Colin Foster <[email-masked]>
> ---
>  drivers/mfd/ocelot-core.c |  9 +++++++++
>  include/soc/mscc/ocelot.h | 12 ++++++++++++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/drivers/mfd/ocelot-core.c b/drivers/mfd/ocelot-core.c
> index a65619a8190b..09132ea52760 100644
> --- a/drivers/mfd/ocelot-core.c
> +++ b/drivers/mfd/ocelot-core.c
> @@ -94,6 +94,15 @@ static struct regmap *ocelot_mfd_regmap_init(struct ocelot_mfd_core *core,
>  	return regmap;
>  }
>  
> +struct regmap *ocelot_mfd_get_regmap_from_resource(struct device *dev,
> +						   const struct resource *res)
> +{
> +	struct ocelot_mfd_core *core = dev_get_drvdata(dev);
> +
> +	return ocelot_mfd_regmap_init(core, res);
> +}
> +EXPORT_SYMBOL(ocelot_mfd_get_regmap_from_resource);

This is almost certainly not the right way to do whatever it is you're
trying to do!

Please don't try to upstream "somewhat a hack"s into the Mainline
kernel.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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