linux-kernel - Re: [PATCH v1 3/4] drm/ls2kbmc: Add support for Loongson-2K BMC display

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Message-ID: <390c14a5-44fe-4328-bcc4-2aa1384e3ad1@suse.de>
Date: Thu, 2 Jan 2025 14:32:27 +0100
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Binbin Zhou <zhoubb.aaron@...il.com>
Cc: Binbin Zhou <zhoubinbin@...ngson.cn>, Huacai Chen
 <chenhuacai@...ngson.cn>, Lee Jones <lee@...nel.org>,
 Corey Minyard <minyard@....org>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Huacai Chen <chenhuacai@...nel.org>,
 linux-kernel@...r.kernel.org, openipmi-developer@...ts.sourceforge.net,
 dri-devel@...ts.freedesktop.org, Xuerui Wang <kernel@...0n.name>,
 loongarch@...ts.linux.dev, Chong Qiao <qiaochong@...ngson.cn>
Subject: Re: [PATCH v1 3/4] drm/ls2kbmc: Add support for Loongson-2K BMC
 display

Hi


Am 02.01.25 um 13:55 schrieb Binbin Zhou:
> Hi Thomas:
>
> Thanks for your reply.
>
> On Thu, Jan 2, 2025 at 5:07 PM Thomas Zimmermann <tzimmermann@...e.de> wrote:
>> Hi
>>
>>
>> Am 30.12.24 um 10:31 schrieb Binbin Zhou:
>> [...]
>>> +
>>> +static struct platform_driver ls2kbmc_platform_driver = {
>>> +     .driver = {
>>> +             .name = "ls2kbmc-framebuffer",
>> The driver is mostly a copy of simpledrm. Why don't you use
>> "simple-framebuffer" for your device name? You could use simpledrm
>> directly then.
> Ah, indeed, the driver is based on simpledrm.
>
> Initially, I also tried to use simpledrm directly, but it will fail in
> drm memory acquire.

Could you point to the exact call that fails within simpledrm?

> Because although we register the driver in platform form, its memory
> belongs to pci space and we can see the corresponding pci probe and
> resource allocation in Patch-1.

I don't understand. Graphics memory is often located on the PCI bus. 
What is so special about this one?

> Therefore, we need to use aperture_remove_conflicting_pci_devices().

So there is already a device that represents the graphics card? That's 
what you'd remove here? If you only add that MFD device, who owns the 
framebuffer? If it's the PCI device from patch 1 ("ls2k-bmc"), why does 
aperture_remove_conflicting_pci_devices() not remove that device? I'm 
somewhat confused, because the logic in your driver mostly looks like it 
binds to a pre-configured framebuffer, but some of the code doesn't. 
Best regards Thomas

>
> Also, since we are using BMC display, the display will be disconnected
> when BMC reset, at this time we need to push the display data (crtc,
> connector, etc.) manually as shown in Patch-4.
>
> Probably it's not the most suitable way to implement it.
>
>> Best regards
>> Thomas
>>
>>> +     },
>>> +     .probe = ls2kbmc_probe,
>>> +     .remove = ls2kbmc_remove,
>>> +};
>>> +
>>> +module_platform_driver(ls2kbmc_platform_driver);
>>> +
>>> +MODULE_DESCRIPTION("DRM driver for Loongson-2K BMC");
>>> +MODULE_LICENSE("GPL");
>> --
>> --
>> Thomas Zimmermann
>> Graphics Driver Developer
>> SUSE Software Solutions Germany GmbH
>> Frankenstrasse 146, 90461 Nuernberg, Germany
>> GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
>> HRB 36809 (AG Nuernberg)
>>
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)