linux-kernel - Re: [PATCH 3/4] drm/tegra: Add VIC support

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Date:	Fri, 22 May 2015 12:25:29 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Mikko Perttunen <mperttunen@...dia.com>
Cc:	Arto Merilainen <amerilainen@...dia.com>,
	linux-tegra@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, achew@...dia.com, srasal@...dia.com,
	dnibade@...dia.com
Subject: Re: [PATCH 3/4] drm/tegra: Add VIC support

On Thu, May 21, 2015 at 05:40:31PM +0300, Mikko Perttunen wrote:
> On 05/21/2015 04:20 PM, Arto Merilainen wrote:
[...]
> > +static int vic_is_addr_reg(struct device *dev, u32 class, u32 offset, u32 val)
> > +{
> > +	struct vic *vic = dev_get_drvdata(dev);
> > +
> > +	/* handle host class */
> > +	if (class == HOST1X_CLASS_HOST1X) {
> > +		if (offset == 0x2b)
> > +			return true;
> > +		return false;
> 
> "return (offset == 0x2b);" perhaps?

I think this should really be extracted into a separate helper. If we
ever need to take into account additional offsets we would otherwise
have to extend every driver rather than just the helper.

Also I think the 0x2b should be replaced by some symbolic name.
According to the TRM 0x2b is the host1x class method named
NV_CLASS_HOST_INDCTRL_0. Oddly enough that doesn't seem to be an address
register. Instead the address seems to be in the INDOFF2 and INDOFF
methods (0x2c and 0x2d). I also can't tell from the TRM what exactly
these are supposed to do.

Arto, can you clarify?

> > +	if (IS_ERR(vic->rst)) {
> > +		dev_err(&pdev->dev, "cannot get reset\n");
> > +		return PTR_ERR(vic->rst);
> > +	}
> > +
> > +	platform_set_drvdata(pdev, vic);
> > +
> > +	INIT_LIST_HEAD(&vic->client.base.list);
> > +	vic->client.base.ops = &vic_client_ops;
> > +	vic->client.base.dev = dev;
> > +	vic->client.base.class = vic_config->class_id;
> > +	vic->client.base.syncpts = syncpts;
> > +	vic->client.base.num_syncpts = 1;
> > +	vic->dev = dev;
> > +	vic->config = vic_config;
> > +
> > +	INIT_LIST_HEAD(&vic->client.list);
> > +	vic->client.ops = &vic_ops;
> > +
> > +	err = tegra_powergate_sequence_power_up(vic->config->powergate_id,
> > +						vic->clk, vic->rst);
> > +	if (err) {
> > +		dev_err(dev, "cannot turn on the device\n");
> > +		return err;
> > +	}
> > +
> > +	err = host1x_client_register(&vic->client.base);
> > +	if (err < 0) {
> 
> You used 'if (err) {' previously, so maybe also here.

For consistency with other Tegra DRM code these checks should use (at
least where possible) the (err < 0) notation.

Thierry

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