linux-kernel - Re: [RFC v2 2/8] video: tegra: Add syncpoint wait and interrupts

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Message-ID: <20121130072357.GF26474@avionic-0098.adnet.avionic-design.de>
Date:	Fri, 30 Nov 2012 08:23:57 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Terje Bergstrom <tbergstrom@...dia.com>,
	linux-tegra@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC v2 2/8] video: tegra: Add syncpoint wait and interrupts

On Thu, Nov 29, 2012 at 11:41:50AM -0700, Stephen Warren wrote:
> On 11/29/2012 01:44 AM, Thierry Reding wrote:
> > On Mon, Nov 26, 2012 at 03:19:08PM +0200, Terje Bergstrom wrote:
> 
> >> diff --git a/drivers/video/tegra/host/host1x/host1x_intr.c
> >> b/drivers/video/tegra/host/host1x/host1x_intr.c
> > [...]
> >> +/* Spacing between sync registers */ +#define REGISTER_STRIDE 4
> > 
> > Erm... no. The usual way you should be doing this is either make
> > the register definitions account for the stride or use accessors
> > that apply the stride. You should be doing the latter anyway to
> > make accesses. For example:
> > 
> > static inline void host1x_syncpt_writel(struct host1x *host1x, 
> > unsigned long value, unsigned long offset) { writel(value,
> > host1x->regs + SYNCPT_BASE + offset); }
> > 
> > static inline unsigned long host1x_syncpt_readl(struct host1x
> > *host1x, unsigned long offset) { return readl(host1x->regs +
> > SYNCPT_BASE + offset); }
> > 
> > Alternatively, if you want to pass the register index instead of
> > the offset, you can use just multiply the offset in that function:
> > 
> > writel(value, host1x->regs + SYNCPT_BASE + (offset << 2));
> > 
> > The same can also be done with the non-syncpt registers.
> 
> It seems like reasonable documentation to replace "<< 2" with "*
> REGISTER_STRIDE" here.

Given that it is a very common pattern, << 2 seems enough documentation
to me, but sure, if you prefer to be extra explicit that's fine with me.

Thierry

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