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

quoted

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.

Please elaborate on the correct way to do that. What we have here is a
SoC (vsc7514) that has MMIO devices. This SoC has a MIPS CPU and
everything is fine when using it. However, the CPU can be disabled and
the SoC connected to another CPU using SPI or PCIe. What Colin is doing
here is using this SoC over SPI. Don't tell me this is not an MFD

When did anyone say that?

because this is exactly what this is, a single chip with a collection of
devices that are also available separately.

The various drivers for the VSC7514 have been written using regmap
exactly for this use case. The missing piece is probing the devices over
SPI instead of MMIO.

Notice that all of that gets worse when using PCIe on architectures that
don't have device tree support and Clément will submit multiple series
trying to fix that.

Okay, it sounds like I'm missing some information, let's see if we can
get to the bottom of this so that I can provide some informed
guidance.

On 29/12/2021 15:23:59+0000, Lee Jones wrote:

quoted

On Sat, 18 Dec 2021, Colin Foster wrote:

quoted

Child devices need to get a regmap from a resource struct,
specifically from the MFD parent.

Child devices usually fetch the Regmap from a pointer the parent
provides.  Usually via either 'driver_data' or 'platform_data'.

However, we can't do that here because ...

quoted

quoted

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.

However, we can't do that here because ...

quoted

quoted

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 <colin.foster@in-advantage.com>
---
 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);

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