Re: [PATCH v13 07/12] drm: bridge/dw_hdmi: add support for multi-byte register width access

[Andy Yan]

Hi Philipp:
On 2014å12æ01æ 20:04, Philipp Zabel wrote:
> Am Freitag, den 28.11.2014, 17:43 +0800 schrieb Andy Yan:
> > Hi Zabel:
> > On 2014å11æ27æ 00:34, Philipp Zabel wrote:
> > > Am Mittwoch, den 26.11.2014, 21:32 +0800 schrieb Andy Yan:
> > > > On rockchip rk3288, only word(32-bit) accesses are
> > > > permitted for hdmi registers.  Byte width accesses (writeb,
> > > > readb) generate an imprecise external abort.
> > > >
> > > > Signed-off-by: Andy Yan <andy.yan@xxxxxxxxxxxxxx>
> > > >
> > > > ---
> > > >
> > > > Changes in v13: None
> > > > Changes in v12: None
> > > > Changes in v11: None
> > > > Changes in v10: None
> > > > Changes in v9: None
> > > > Changes in v8: None
> > > > Changes in v7: None
> > > > Changes in v6:
> > > > - refactor register access without reg_shift
> > > >
> > > > Changes in v5:
> > > > - refactor reg-io-width
> > > >
> > > > Changes in v4: None
> > > > Changes in v3:
> > > > - split multi-register access to one indepent patch
> > > >
> > > >    drivers/gpu/drm/bridge/dw_hdmi.c | 57 +++++++++++++++++++++++++++++++++++-----
> > > >    1 file changed, 51 insertions(+), 6 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/bridge/dw_hdmi.c b/drivers/gpu/drm/bridge/dw_hdmi.c
> > > > index a53bf63..5e88c8d 100644
> > > > --- a/drivers/gpu/drm/bridge/dw_hdmi.c
> > > > +++ b/drivers/gpu/drm/bridge/dw_hdmi.c
> > > > @@ -100,6 +100,11 @@ struct hdmi_data_info {
> > > >    	struct hdmi_vmode video_mode;
> > > >    };
> > > >    
> > > > +union dw_reg_ptr {
> > > > +	u32 __iomem *p32;
> > > > +	u8 __iomem *p8;
> > > > +};
> > > I see no need to introduce this. Just explicitly multiply the offset in
> > > dw_hdmi_writel.
> >       Is there any disadvantage to do like this?
> >       The compiler can help us do the explicitly multiply by this way.
> Four additional lines, a new defined type, a few more changes to struct
> dw_hdmi and dw_hdmi_bind necessary.
>
> Technically I see no problem to let the compiler do the multiplication,
> my issue is that it ever so slightly obfuscates the code. Instead of
> just writing "* 4" in two functions, we get a new union that you need to
> know about when looking at struct dw_hdmi and dw_hdmi_bind, regs.p8 is
> used but never assigned directly, it's just a tiny bit of additional
> effort needed to understand the code. But when the cost to avoid that is
> so small...
>
> regards
> Philipp

  What you said is right, I will change it in PATCH V15
   thanks .
> _______________________________________________
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> Linux-rockchip@xxxxxxxxxxxxxxxxxxx
> http://lists.infradead.org/mailman/listinfo/linux-rockchip


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