linux-kernel - Re: On register r/w macros/procedures of drivers/media/pci

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Date:	Sun, 19 Apr 2015 11:55:57 +0300
From:	Andrey Utkin <andrey.utkin@...p.bluecherry.net>
To:	Hans Verkuil <hverkuil@...all.nl>
Cc:	Linux Media <linux-media@...r.kernel.org>,
	"kernel-mentors@...enic.com" <kernel-mentors@...enic.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hans.verkuil" <hans.verkuil@...co.com>, khalasa <khalasa@...p.pl>
Subject: Re: On register r/w macros/procedures of drivers/media/pci

On Sun, Apr 19, 2015 at 11:28 AM, Hans Verkuil <hverkuil@...all.nl> wrote:
> Check the types of llmio and bbmio:
>
>         u32                     __iomem *lmmio;
>         u8                      __iomem *bmmio;
>
> So the values of the pointers are the same, but the types are not.
>
> So 'lmmio + 1' == 'bmmio + sizeof(u32)' == 'bbmio + 4'.
>
> Since all the registers are defined as byte offsets relative to the start
> of the memory map you cannot just do 'lmmio + reg' since that would be a
> factor 4 off. Instead you have to divide by 4 to get it back in line.
>
> Frankly, I don't think lmmio is necessary at all since readl/writel don't
> need a u32 pointer at all since they use void pointers. I never noticed
> that when I cleaned up the tw68 driver. Using 'void __iomem *mmio' instead
> of lmmio/bmmio and dropping the shifts in the tw_ macros would work just
> as well.

>
> Hope this helps,

Oh, indeed, I have forgot this basic thing of pointer arithmetics.
Thanks a lot for elaboration and the proposed solution.

-- 
Bluecherry developer.
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