linux-kernel - Re: [PATCH v3 4/9] PCI/VGA: Improve the default VGA device selection

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Message-ID: <42658701-fa7d-1206-abae-5a1e01c060e3@loongson.cn>
Date:   Mon, 24 Jul 2023 20:28:50 +0800
From:   suijingfeng <suijingfeng@...ngson.cn>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Sui Jingfeng <sui.jingfeng@...ux.dev>
Cc:     David Airlie <airlied@...il.com>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, kvm@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-fbdev@...r.kernel.org,
        Alex Deucher <alexander.deucher@....com>,
        Christian Konig <christian.koenig@....com>,
        Pan Xinhui <Xinhui.Pan@....com>,
        Daniel Vetter <daniel@...ll.ch>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        Karol Herbst <kherbst@...hat.com>,
        Lyude Paul <lyude@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Hawking Zhang <Hawking.Zhang@....com>,
        Mario Limonciello <mario.limonciello@....com>,
        Lijo Lazar <lijo.lazar@....com>,
        YiPeng Chai <YiPeng.Chai@....com>,
        Bokun Zhang <Bokun.Zhang@....com>,
        Likun Gao <Likun.Gao@....com>,
        Ville Syrjala <ville.syrjala@...ux.intel.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Kevin Tian <kevin.tian@...el.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Yishai Hadas <yishaih@...dia.com>,
        Abhishek Sahu <abhsahu@...dia.com>,
        Yi Liu <yi.l.liu@...el.com>,
        Jani Nikula <jani.nikula@...el.com>
Subject: Re: [PATCH v3 4/9] PCI/VGA: Improve the default VGA device selection

Hi,


Thanks for you noticed my change.


On 2023/7/20 03:32, Bjorn Helgaas wrote:
>> @@ -1509,13 +1543,24 @@ static int pci_notify(struct notifier_block *nb, unsigned long action,
>>   	 * cases of hotplugable vga cards.
>>   	 */
>>   
>> -	if (action == BUS_NOTIFY_ADD_DEVICE)
>> +	switch (action) {
>> +	case BUS_NOTIFY_ADD_DEVICE:
>>   		notify = vga_arbiter_add_pci_device(pdev);
>> -	else if (action == BUS_NOTIFY_DEL_DEVICE)
>> +		if (notify)
>> +			vga_arbiter_notify_clients();
>> +		break;
>> +	case BUS_NOTIFY_DEL_DEVICE:
>>   		notify = vga_arbiter_del_pci_device(pdev);
>> +		if (notify)
>> +			vga_arbiter_notify_clients();
>> +		break;
>> +	case BUS_NOTIFY_BOUND_DRIVER:
>> +		vga_arbiter_do_arbitration(pdev);
>> +		break;
>> +	default:
>> +		break;
>> +	}
> Changing from if/else to switch makes the patch bigger than necessary
> for no real benefit and obscures what is really changing.

Actually, the logic become more clear after this patch applied.

```

     switch (action) {
     case BUS_NOTIFY_ADD_DEVICE:
         notify = vga_arbiter_add_pci_device(pdev);
         if (notify)
             vga_arbiter_notify_clients();
         break;
     case BUS_NOTIFY_DEL_DEVICE:
         notify = vga_arbiter_del_pci_device(pdev);
         if (notify)
             vga_arbiter_notify_clients();
         break;
     case BUS_NOTIFY_BOUND_DRIVER:
         vga_arbiter_do_arbitration(pdev);
         break;
     default:
         break;
     }

```


Because we only need call vga_arbiter_notify_clients() when action == 
BUS_NOTIFY_ADD_DEVICE or action == BUS_NOTIFY_DEL_DEVICE,

But *NOT* when the action equals to  BUS_NOTIFY_BOUND_DRIVER.