On 09-09-20, 08:48, Pierre-Louis Bossart wrote:
>
> > > > > + * 25 0 (Reserved)
> > > > > + * 24:22 Function Number [2:0]
> > > > > + * 21 Entity[6]
> > > > > + * 20:19 Control Selector[5:4]
> > > > > + * 18 0 (Reserved)
> > > > > + * 17:15 Control Number[5:3]
> > > > > + * 14 Next
> > > > > + * 13 MBQ
> > > > > + * 12:7 Entity[5:0]
> > > > > + * 6:3 Control Selector[3:0]
> > > > > + * 2:0 Control Number[2:0]
> > > > > + */
> > > > > +
> > > > > +#define SDW_SDCA_CTL(fun, ent, ctl, ch) \
> > > > > + (BIT(30) | \
> > > >
> > > > Programmatically this is fine, but then since we are defining for the
> > > > description above, IMO it would actually make sense for this to be defined
> > > > as FIELD_PREP:
> > > >
> > > > FIELD_PREP(GENMASK(30, 26), 1)
> > > >
> > > > or better
> > > >
> > > > u32_encode_bits(GENMASK(30, 26), 1)
> > > >
> > > > > + FIELD_PREP(GENMASK(24, 22), FIELD_GET(GENMASK(2, 0), (fun))) | \
> > > >
> > > > Why not use u32_encode_bits(GENMASK(24, 22), (fun)) instead for this and
> > > > below?
> > >
> > > Because your comment for the v1 review was to use FIELD_PREP/FIELD_GET, and
> > > your other patches for bitfield access only use FIELD_PREP/FIELD_GET.
> >
> > yes and looking at this, I feel u32_encode_bits(GENMASK(24, 22), (fun))
> > would look better than FIELD_PREP(GENMASK(24, 22), FIELD_GET(GENMASK(2, 0), (fun)))
> >
> > Do you agree?
>
> The Function (fun) case is the easy one: the value is not split in two.
>
> But look at the entity case, it's split in two:
>
> FIELD_PREP(BIT(21), FIELD_GET(BIT(6), (ent))) FIELD_PREP(GENMASK(12, 7),
> FIELD_GET(GENMASK(5, 0), (ent)))
>
> same for control
>
> FIELD_PREP(GENMASK(20, 19), FIELD_GET(GENMASK(5, 4), (ctl))) |
> FIELD_PREP(GENMASK(6, 3), FIELD_GET(GENMASK(3, 0), (ctl))) |
>
> and same for channel number
>
> FIELD_PREP(GENMASK(17, 15), FIELD_GET(GENMASK(5, 3), (ch))) |
> FIELD_PREP(GENMASK(2, 0), FIELD_GET(GENMASK(2, 0), (ch))))
>
> I don't see how we can avoid using the FIELD_GET to extract the relevant
> bits from entity, control, channel number values.
No, you dont need FIELD_GET, that would be pointless for this helper if
that was the case
>
> Or I am missing your point completely.
Correct
It should be:
foo |= u32_encode_bits(val, FOO_MASK_A);
which would write val into bits represented by FOO_MASK_A by
appropriately shifting val and masking it with FOO_MASK_A
So net result is bits in FOO_MASK_A are modified with val, rest of the
bits are not touched
>
>
> > > > And while at it, consider defining masks for various fields rather than
> > > > using numbers in GENMASK() above, that would look better, be more
> > > > readable and people can reuse it.
> > >
> > > Actually on this one I disagree. These fields are not intended to be used by
> > > anyone, the goal is precisely to hide them behind regmap, and the use of raw
> > > numbers makes it easier to cross-check the documentation and the code.
> > > Adding a separate set of definitions would not increase readability.
> >
> > Which one would you prefer:
> >
> > #define SDCA_FUN_MASK GENMASK(24, 22)
> >
> > foo |= u32_encode_bits(SDCA_FUN_MASK, fun)
> >
> > Or the one proposed...?
>
> Same as above, let's see what this does with the control case where we'd
> need to have four definitions:
>
> #define SDCA_CONTROL_DEST_MASK1 GENMASK(20, 19)
> #define SDCA_CONTROL_ORIG_MASK1 GENMASK(5, 4)
> #define SDCA_CONTROL_DEST_MASK2 GENMASK(6, 3)
> #define SDCA_CONTROL_ORIG_MASK2 GENMASK(3, 0)
>
> And the code would look like
>
> foo |= u32_encode_bits(SDCA_CONTROL_DEST_MASK1,
> FIELD_GET(SDCA_CONTROL_ORIG_MASK1, fun));
> foo |= u32_encode_bits(SDCA_CONTROL_DEST_MASK2,
> FIELD_GET(SDCA_CONTROL_ORIG_MASK2, fun));
>
> The original suggestion was:
>
> FIELD_PREP(GENMASK(20, 19), FIELD_GET(GENMASK(5, 4), (ctl))) |
> FIELD_PREP(GENMASK(6, 3), FIELD_GET(GENMASK(3, 0), (ctl))) |
>
> I prefer the original... Adding these defines doesn't really add value
> because
> a) the values will not be reused anywhere else.
> b) we need 12 of those defines
> b) we need a prefix for those defines which makes the code heavier
--
~Vinod
