Re: [PATCH v11 net-next 1/9] mfd: ocelot: add helper to get regmap from a resource

Colin Foster
2022-06-28T17:26:49Z

Hi Vladimir,

On Tue, Jun 28, 2022 at 04:08:10PM +0000, Vladimir Oltean wrote:
> On Tue, Jun 28, 2022 at 01:17:01AM -0700, Colin Foster wrote:
> > diff --git a/include/linux/mfd/ocelot.h b/include/linux/mfd/ocelot.h
> > new file mode 100644
> > index 000000000000..5c95e4ee38a6
> > --- /dev/null
> > +++ b/include/linux/mfd/ocelot.h
> > @@ -0,0 +1,27 @@
> > +/* SPDX-License-Identifier: GPL-2.0 OR MIT */
> > +/* Copyright 2022 Innovative Advantage Inc. */
> > +
> > +#include <linux/err.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/regmap.h>
> > +#include <linux/types.h>
> > +
> > +struct resource;
> > +
> > +static inline struct regmap *
> > +ocelot_platform_init_regmap_from_resource(struct platform_device *pdev,
> > + unsigned int index,
> > + const struct regmap_config *config)
>
> I think this function name is too long (especially if you're going to
> also introduce ocelot_platform_init_regmap_from_resource_optional),
> and I have the impression that the "platform_init_" part of the name
> doesn't bring too much value. How about ocelot_regmap_from_resource()?

I thought the same thing after your first email. My thought was "how do
I indent that?" :-)

>
> > +{
> > + struct resource *res;
> > + u32 __iomem *regs;
> > +
> > + regs = devm_platform_get_and_ioremap_resource(pdev, index, &res);
> > +
> > + if (!res)
> > + return ERR_PTR(-ENOENT);
> > + else if (IS_ERR(regs))
> > + return ERR_CAST(regs);
> > + else
> > + return devm_regmap_init_mmio(&pdev->dev, regs, config);
> > +}
> > --
> > 2.25.1
> >
>
> To illustrate what I'm trying to say, these would be the shim
> definitions:
>
> static inline struct regmap *
> ocelot_regmap_from_resource(struct platform_device *pdev,
> unsigned int index,
> const struct regmap_config *config)
> {
> struct resource *res;
> void __iomem *regs;
>
> regs = devm_platform_get_and_ioremap_resource(pdev, index, &res);
> if (IS_ERR(regs))
> return regs;
>
> return devm_regmap_init_mmio(&pdev->dev, regs, config);
> }
>
> static inline struct regmap *
> ocelot_regmap_from_resource_optional(struct platform_device *pdev,
> unsigned int index,
> const struct regmap_config *config)
> {
> struct resource *res;
> void __iomem *regs;
>
> res = platform_get_resource(pdev, IORESOURCE_MEM, index);
> if (!res)
> return NULL;
>
> regs = devm_ioremap_resource(&pdev->dev, r);
> if (IS_ERR(regs))
> return regs;
>
> return devm_regmap_init_mmio(&pdev->dev, regs, config);
> }
>
> and these would be the full versions:
>
> static struct regmap *
> ocelot_regmap_from_mem_resource(struct device *dev, struct resource *res,
> const struct regmap_config *config)
> {
> void __iomem *regs;
>
> regs = devm_ioremap_resource(dev, r);
> if (IS_ERR(regs))
> return regs;
>
> return devm_regmap_init_mmio(dev, regs, config);
> }
>
> static struct regmap *
> ocelot_regmap_from_reg_resource(struct device *dev, struct resource *res,
> const struct regmap_config *config)
> {
> /* Open question: how to differentiate SPI from I2C resources? */

My expectation is to set something up in drivers/mfd/ocelot-{spi,i2c}.c
and have an if/else / switch. PCIe might actually be our first hardware
spin.

> return ocelot_spi_init_regmap(dev->parent, dev, res);
> }
>
> struct regmap *
> ocelot_regmap_from_resource_optional(struct platform_device *pdev,
> unsigned int index,
> const struct regmap_config *config)
> {
> struct device *dev = &pdev->dev;
> struct resource *res;
>
> res = platform_get_resource(pdev, IORESOURCE_MEM, index);
> if (res)
> return ocelot_regmap_from_mem_resource(dev, res, config);
>
> /*
> * Fall back to using IORESOURCE_REG, which is possible in an
> * MFD configuration
> */
> res = platform_get_resource(pdev, IORESOURCE_REG, index);
> if (res)
> return ocelot_regmap_from_reg_resource(dev, res, config);
>
> return NULL;
> }
>
> struct regmap *
> ocelot_regmap_from_resource(struct platform_device *pdev,
> unsigned int index,
> const struct regmap_config *config)
> {
> struct regmap *map;
>
> map = ocelot_regmap_from_resource_optional(pdev, index, config);
> return map ? : ERR_PTR(-ENOENT);
> }
>
> I hope I didn't get something wrong, this is all code written within the
> email client, so it is obviously not compiled/tested....

Yep - I definitely get the point. And thanks for the review.

The other (bigger?) issue is around how this MFD can be loaded as a
module. Right now it is pretty straightforward to say
#if IS_ENABLED(CONFIG_MFD_OCELOT). Theres a level of nuance if
CONFIG_MFD_OCELOT=m while the child devices are compiled in
(CONFIG_PINCTRL_MICROCHIP_SGPIO=y for example). It still feels like this
code belongs somewhere in platform / resource / device / mfd...?

It might be perfectly valid to have multiple SGPIO controllers - one
local and one remote / SPI. But without the CONFIG_MFD_OCELOT module
loaded, I don't think the SGPIO module would work.

This patch set deals with the issue by setting MFD_OCELOT to a boolean -
but in the long run I think a module makes sense. I admittedly haven't
spent enough time researching (bashing my head against the wall) this,
but this seems like a good opportunity to at least express that I'm
expecting to have to deal with this issue soon. I met with Alexandre at
ELC this past week, and he said Arnd (both added to CC) might be a good
resource - but again I'd like to do a little more searching before
throwing it over the wall.