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SubjectRe: [RFC v1 2/2] regmap: allow a defined reg_base to be added to every address
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
> >


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