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Date:   Mon, 14 Mar 2022 08:37:14 -0700
From:   Colin Foster <colin.foster@in-advantage.com>
To:     Mark Brown <broonie@kernel.org>
Cc:     linux-kernel@vger.kernel.org,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [RFC v1 2/2] regmap: allow a defined reg_base to be added to
 every address
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On Mon, Mar 14, 2022 at 08:28:36AM +0000, Mark Brown wrote:
> On Sun, Mar 13, 2022 at 03:45:24PM -0700, Colin Foster wrote:
> 
> > There's an inconsistency that arises when a register set can be accessed
> > internally via MMIO, or externally via SPI. The VSC7514 chip allows both
> > modes of operation. When internally accessed, the system utilizes __iomem,
> > devm_ioremap_resource, and devm_regmap_init_mmio.
> 
> > For SPI it isn't possible to utilize memory-mapped IO. To properly operate,
> > the resource base must be added to the register before every operation.
> 
> The problem here isn't the mixed buses, the problem is that the hardware
> designers have for some unknown reason decided to not use the same
> register addresses on the two buses which just seems pointlessly
> unhelpful.

That is true for the address downshift. But the resource start
seemingly still needs to be addressed somewhere. Currently that is
contained on a per-regmap basis inside my WIP drivers/mfd/ocelot-spi.c.
But that falls apart as soon as regmap_bus gets involved, as I'm finding
out.

So would it make sense to keep this patch, drop the downshift, and
re-define the offsets / stride to match the modified address space?

> 
> > 
> > Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
> > ---
> >  drivers/base/regmap/internal.h | 1 +
> >  drivers/base/regmap/regmap.c   | 6 ++++++
> >  include/linux/regmap.h         | 3 +++
> >  3 files changed, 10 insertions(+)
> > 
> > diff --git a/drivers/base/regmap/internal.h b/drivers/base/regmap/internal.h
> > index 88f710e7ce31..b4df36c7b17d 100644
> > --- a/drivers/base/regmap/internal.h
> > +++ b/drivers/base/regmap/internal.h
> > @@ -63,6 +63,7 @@ struct regmap {
> >  	regmap_unlock unlock;
> >  	void *lock_arg; /* This is passed to lock/unlock functions */
> >  	gfp_t alloc_flags;
> > +	unsigned int reg_base;
> >  
> >  	struct device *dev; /* Device we do I/O on */
> >  	void *work_buf;     /* Scratch buffer used to format I/O */
> > diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
> > index 1c7c6d6361af..5e12f7cb5147 100644
> > --- a/drivers/base/regmap/regmap.c
> > +++ b/drivers/base/regmap/regmap.c
> > @@ -821,6 +821,8 @@ struct regmap *__regmap_init(struct device *dev,
> >  	else
> >  		map->alloc_flags = GFP_KERNEL;
> >  
> > +	map->reg_base = config->reg_base;
> > +
> >  	map->format.reg_bytes = DIV_ROUND_UP(config->reg_bits, 8);
> >  	map->format.pad_bytes = config->pad_bits / 8;
> >  	map->format.reg_downshift = config->reg_downshift;
> > @@ -1736,6 +1738,7 @@ static int _regmap_raw_write_impl(struct regmap *map, unsigned int reg,
> >  			return ret;
> >  	}
> >  
> > +	reg += map->reg_base;
> >  	reg >>= map->format.reg_downshift;
> >  	map->format.format_reg(map->work_buf, reg, map->reg_shift);
> >  	regmap_set_work_buf_flag_mask(map, map->format.reg_bytes,
> > @@ -1907,6 +1910,7 @@ static int _regmap_bus_formatted_write(void *context, unsigned int reg,
> >  			return ret;
> >  	}
> >  
> > +	reg += map->reg_base;
> >  	reg >>= map->format.reg_downshift;
> >  	map->format.format_write(map, reg, val);
> >  
> > @@ -2349,6 +2353,7 @@ static int _regmap_raw_multi_reg_write(struct regmap *map,
> >  		unsigned int reg = regs[i].reg;
> >  		unsigned int val = regs[i].def;
> >  		trace_regmap_hw_write_start(map, reg, 1);
> > +		reg += map->reg_base;
> >  		reg >>= map->format.reg_downshift;
> >  		map->format.format_reg(u8, reg, map->reg_shift);
> >  		u8 += reg_bytes + pad_bytes;
> > @@ -2677,6 +2682,7 @@ static int _regmap_raw_read(struct regmap *map, unsigned int reg, void *val,
> >  			return ret;
> >  	}
> >  
> > +	reg += map->reg_base;
> >  	reg >>= map->format.reg_downshift;
> >  	map->format.format_reg(map->work_buf, reg, map->reg_shift);
> >  	regmap_set_work_buf_flag_mask(map, map->format.reg_bytes,
> > diff --git a/include/linux/regmap.h b/include/linux/regmap.h
> > index 40fb9399add6..de81a94d7b30 100644
> > --- a/include/linux/regmap.h
> > +++ b/include/linux/regmap.h
> > @@ -239,6 +239,8 @@ typedef void (*regmap_unlock)(void *);
> >   *              used.
> >   * @reg_downshift: The number of bits to downshift the register before
> >   *		   performing any operations.
> > + * @reg_base: Value to be added to every register address before performing any
> > + *	      operation.
> >   * @pad_bits: Number of bits of padding between register and value.
> >   * @val_bits: Number of bits in a register value, mandatory.
> >   *
> > @@ -363,6 +365,7 @@ struct regmap_config {
> >  	int reg_bits;
> >  	int reg_stride;
> >  	int reg_downshift;
> > +	unsigned int reg_base;
> >  	int pad_bits;
> >  	int val_bits;
> >  
> > -- 
> > 2.25.1
> >