linux-kernel - Re: [PATCH v11 7/7] drm/lsdc: add drm driver for loongson display controller

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Date:   Thu, 24 Mar 2022 08:56:25 -0500
From:   Rob Herring <robh@...nel.org>
To:     Sui Jingfeng <15330273260@....cn>
Cc:     Qing Zhang <zhangqing@...ngson.cn>,
        David Airlie <airlied@...ux.ie>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        linux-kernel@...r.kernel.org, Sam Ravnborg <sam@...nborg.org>,
        kernel test robot <lkp@...el.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        devicetree@...r.kernel.org, suijingfeng <suijingfeng@...ngson.cn>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Roland Scheidegger <sroland@...are.com>,
        Andrey Zhizhikin <andrey.zhizhikin@...ca-geosystems.com>,
        dri-devel@...ts.freedesktop.org,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-mips@...r.kernel.org,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH v11 7/7] drm/lsdc: add drm driver for loongson display
 controller

On Thu, Mar 24, 2022 at 03:32:01PM +0800, Sui Jingfeng wrote:
> 
> On 2022/3/23 04:49, Rob Herring wrote:
> > > +	}
> > > +
> > > +	spin_lock_init(&li2c->reglock);
> > > +
> > > +	snprintf(compat, sizeof(compat), "lsdc,i2c-gpio-%d", index);
> > compatible values shouldn't have an index and you shouldn't need a
> > index in DT. You need to iterate over child nodes with matching
> > compatible.
> 
> Why compatible values shouldn't have an index, does devicetree
> specification prohibit this? [1]

Probably not explicitly, but that's fundamentally not how compatible 
works. 'compatible' defines WHAT the device is, not WHICH device and 
that is used for matching devices to drivers. Drivers work on multiple 
instances.

> The recommended format is "manufacturer,model", where manufacturer is a string describing the name
> of the manufacturer (such as a stock ticker symbol), and model specifies the model number. [1]

I don't see anything saying to put the instance in there, do you?

> 
> [1] https://www.devicetree.org/specifications/
>