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 16:49:15 +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:
>> +/*
>> + * ls7a_gpio_i2c_set - set the state of a gpio pin indicated by mask
>> + * @mask: gpio pin mask
>> + */
>> +static void ls7a_gpio_i2c_set(struct lsdc_i2c * const li2c, int mask, int state)
>> +{
>> +	unsigned long flags;
>> +	u8 val;
>> +
>> +	spin_lock_irqsave(&li2c->reglock, flags);
> What are you protecting? Doesn't the caller serialize calls to these
> functions?
>
This driver is ported from my work from my downstream work.

Maxime also ask this question before, but i did not answer.
He is right, protect single register access is not necessary.
uncached access have done the job itself.
so i remove it in V11 of my patch set.

There are two way GPIO emulated i2c, I want the code between
spin_lock_irqsave(&li2c->reglock, flags) and spin_unlock_irqrestore(&li2c->reglock, flags);
finished in a atomic way, without any disruption.

The two i2c should not have any influence each other.
I write it by gut feeling, and luckily it works very well in practice.