Re: [PATCH v4 2/4] mmc: dw_mmc-rockchip: Add internal phase support

[Dragan Simic <dsimic@manjaro.org>]

Hello Detlev,

On 2024-08-23 15:34, Detlev Casanova wrote:
> On Friday, 23 August 2024 01:41:44 EDT Dragan Simic wrote:
>> Hello Detlev,
>> 
>> Please see a comment below.
>> 
>> On 2024-08-22 23:15, Detlev Casanova wrote:
>> > From: Shawn Lin <shawn.lin@rock-chips.com>
>> >
>> > Some Rockchip devices put the phase settings into the dw_mmc
>> > controller.
>> >
>> > When the feature is present, the ciu-drive and ciu-sample clocks are
>> > not used and the phase configuration is done directly through the mmc
>> > controller.
>> >
>> > Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
>> > Signed-off-by: Detlev Casanova <detlev.casanova@collabora.com>
>> > Acked-by: Shawn Lin <shawn.lin@rock-chips.com>
>> > ---
>> >
>> >  drivers/mmc/host/dw_mmc-rockchip.c | 171 +++++++++++++++++++++++++++--
>> >  1 file changed, 160 insertions(+), 11 deletions(-)
>> >
>> > diff --git a/drivers/mmc/host/dw_mmc-rockchip.c
>> > b/drivers/mmc/host/dw_mmc-rockchip.c
>> > index b07190ba4b7a..2748f9bf2691 100644
>> > --- a/drivers/mmc/host/dw_mmc-rockchip.c
>> > +++ b/drivers/mmc/host/dw_mmc-rockchip.c
>> > @@ -15,7 +15,17 @@
>> >
>> >  #include "dw_mmc.h"
>> >  #include "dw_mmc-pltfm.h"
>> >
>> > -#define RK3288_CLKGEN_DIV	2
>> > +#define RK3288_CLKGEN_DIV		2
>> > +#define SDMMC_TIMING_CON0		0x130
>> > +#define SDMMC_TIMING_CON1		0x134
>> > +#define ROCKCHIP_MMC_DELAY_SEL		BIT(10)
>> > +#define ROCKCHIP_MMC_DEGREE_MASK	0x3
>> > +#define ROCKCHIP_MMC_DEGREE_OFFSET	1
>> > +#define ROCKCHIP_MMC_DELAYNUM_OFFSET	2
>> > +#define ROCKCHIP_MMC_DELAYNUM_MASK	(0xff <<
>> > ROCKCHIP_MMC_DELAYNUM_OFFSET)
>> > +#define ROCKCHIP_MMC_DELAY_ELEMENT_PSEC	60
>> > +#define HIWORD_UPDATE(val, mask, shift) \
>> > +		((val) << (shift) | (mask) << ((shift) + 16))
>> >
>> >  static const unsigned int freqs[] = { 100000, 200000, 300000, 400000
>> >
>> > };
>> >
>> > @@ -24,8 +34,143 @@ struct dw_mci_rockchip_priv_data {
>> >
>> >  	struct clk		*sample_clk;
>> >  	int			default_sample_phase;
>> >  	int			num_phases;
>> >
>> > +	int			internal_phase;
>> >
>> >  };
>> 
>> It might be good to declare internal_phase as "unsigned int
>> internal_phase:1",
>> i.e. as a bit field, which isn't going to save some memory in this
>> particular
>> case, but it would show additional attention to detail.
> 
> In that case, I would go with a bool instead of int, that makes things
> even clearer.

My suggestion to use "unsigned int internal_phase:1" actually takes
inspiration from the ASoC code, in which such bit fields are used
quite a lot, even when using them actually doesn't save space.

In this particular case, using plain bool would make sense, but I
still think that using an "unsigned int internal_phase:1" bit field
would fit better, because it would show the intention to possibly
save a bit of RAM at some point.  OTOH, I don't think that using
bool with such bit fields would actually work cleanly, because bool
actually resolves to int that's a signed type.