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Date:   Fri, 20 Jan 2023 10:41:17 +0100
From:   "s.hauer@pengutronix.de" <s.hauer@pengutronix.de>
To:     "Sverdlin, Alexander" <alexander.sverdlin@siemens.com>
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        "michael.riesch@wolfvision.net" <michael.riesch@wolfvision.net>,
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        "daniel@ffwll.ch" <daniel@ffwll.ch>,
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Subject: Re: [PATCH 1/3] drm/rockchip: lvds: add rk3568 support
Message-ID: <20230120094117.GM24755@pengutronix.de>
References: <20230119184807.171132-1-a1ba.omarov@gmail.com>
 <20230119184807.171132-2-a1ba.omarov@gmail.com>
 <20230120091641.GL24755@pengutronix.de>
 <9fe2678da0ae10e6996889971a3137799a68c4b9.camel@siemens.com>
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On Fri, Jan 20, 2023 at 09:31:43AM +0000, Sverdlin, Alexander wrote:
> Hello Sascha,
> 
> On Fri, 2023-01-20 at 10:16 +0100, Sascha Hauer wrote:
> > > +???????/* Enable LVDS mode */
> > > +???????return regmap_update_bits(lvds->grf, RK3568_GRF_VO_CON2,
> > > +???????????????????????????????? RK3568_LVDS0_MODE_EN(1),
> > > +???????????????????????????????? RK3568_LVDS0_MODE_EN(1));
> > 
> > Isn't this the same as:
> > 
> > ????????regmap_write(lvds->grf, RK3568_GRF_VO_CON2,
> > RK3568_LVDS0_MODE_EN(1));
> > 
> > Unless I am missing something I find a plain regmap_write() easier to
> > read.
> 
> the former is setting a bit in a RMW operation, the latter is a plain
> write, isn't it?

That's right from the view what the function itself does. Note the
registers that are accessed here are a bit special. They effectively
are 16bit wide, the upper 16bit contain a mask. Only the bits set in the
mask are actually modified in the lower bits. See the register bit
definitions:

#define HIWORD_UPDATE(v, h, l)  ((GENMASK(h, l) << 16) | ((v) << (l)))

#define   RK3568_LVDS0_SELECT(val)             HIWORD_UPDATE(val,  5, 4)

Sascha

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