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

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Date:   Wed, 23 Mar 2022 12:12:43 +0800
From:   Sui Jingfeng <15330273260@....cn>
To:     Rob Herring <robh@...nel.org>
Cc:     Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Roland Scheidegger <sroland@...are.com>,
        Zack Rusin <zackr@...are.com>,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Andrey Zhizhikin <andrey.zhizhikin@...ca-geosystems.com>,
        Sam Ravnborg <sam@...nborg.org>,
        "David S . Miller" <davem@...emloft.net>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Ilia Mirkin <imirkin@...m.mit.edu>,
        Qing Zhang <zhangqing@...ngson.cn>,
        suijingfeng <suijingfeng@...ngson.cn>,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v11 7/7] drm/lsdc: add drm driver for loongson display
 controller


On 2022/3/23 04:49, Rob Herring wrote:
>> +/*
>> + * mainly for dc in ls7a1000 which have builtin gpio emulated i2c
>> + *
>> + * @index : output channel index, 0 for DVO0, 1 for DVO1
>> + */
>> +struct lsdc_i2c *lsdc_create_i2c_chan(struct device *dev, void *base, unsigned int index)
>> +{
>> +	char compat[32] = {0};
>> +	unsigned int udelay = 5;
>> +	unsigned int timeout = 2200;
>> +	int nr = -1;
>> +	struct i2c_adapter *adapter;
>> +	struct lsdc_i2c *li2c;
>> +	struct device_node *i2c_np;
>> +	int ret;
>> +
>> +	li2c = devm_kzalloc(dev, sizeof(*li2c), GFP_KERNEL);
>> +	if (!li2c)
>> +		return ERR_PTR(-ENOMEM);
>> +
>> +	li2c->index = index;
>> +	li2c->dev = dev;
>> +
>> +	if (index == 0) {
>> +		li2c->sda = 0x01;
>> +		li2c->scl = 0x02;
>> +	} else if (index == 1) {
>> +		li2c->sda = 0x04;
>> +		li2c->scl = 0x08;
> Just require this to be in DT rather than having some default.
>
By design,  I am try very hard to let the code NOT fully  DT dependent. DT is nice , easy to learn and use.
But kernel side developer plan to follow UEFI + ACPI Specification on LS3A5000 + LS7A1000 platform. See [1]
There will no DT support then, provide a convention support  make the driver more flexible. I want the
driver works with minimal requirement. The driver just works on simple boards by put the following dc device
node in arch/mips/dts/loongson/loongson64g_4core_ls7a.dts,

             lsdc: display-controller@6,1 {
                 compatible = "loongson,ls7a1000-dc";

                 reg = <0x3100 0x0 0x0 0x0 0x0>;
                 interrupts = <28 IRQ_TYPE_LEVEL_HIGH>;
                 interrupt-parent = <&pic>;
             };

[1] 
https://lwn.net/Articles/869541/#:~:text=LoongArch%20is%20a%20new%20RISC%20ISA%2C%20which%20is,revision%20of%20ACPI%20Specification%20%28current%20revision%20is%206.4%29.