linux-kernel - Re: [PATCH 1/1] gpu: drm: fix compilation errors in drm_vram

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Message-ID: <57ec4e5a-64a9-4e44-9304-d41e6148da01@suse.de>
Date: Wed, 13 Aug 2025 09:22:50 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Gary Chu(楚光庆) <chuguangqing@...pur.com>,
 "maarten.lankhorst@...ux.intel.com" <maarten.lankhorst@...ux.intel.com>,
 "mripard@...nel.org" <mripard@...nel.org>,
 "airlied@...il.com" <airlied@...il.com>, "simona@...ll.ch" <simona@...ll.ch>
Cc: "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] gpu: drm: fix compilation errors in drm_vram_helper

Hi

Am 13.08.25 um 08:58 schrieb Thomas Zimmermann:
> Hi
>
> Am 13.08.25 um 03:38 schrieb Gary Chu(楚光庆):
>> Hi Thomas
>>
>> This is what I've done in the yhgch_drm driver.
>> See the link below:
>> https://lore.kernel.org/all/20250808053508.52202-1-chuguangqing@inspur.com/T/#t 
>>
>
> I see. I thought it was for an existing driver. In new drivers, please 
> don't use VRAM helpers any longer. VRAM helpers are based on TTM and 
> new drivers should use TTM directly. If you integrate the code from 
> VRAM helpers into your driver, you should be good.
>
> Note that for reliably using TTM, your hardware requires at least 3 
> times the memory as the largest resolution+depth requires. The driver 
> says 1920*1200@...pp, which amounts to ~9 MiB of VRAM. For TTM usage, 
> your device requires at least 32 MiB of VRAM available.
>
> If your devices have smaller VRAM, rather use GEM SHMEM helpers instead.

And with TTM, buffer sharing is fairly hard to impossible. Shmem or DMA 
helpers provide it out of the box.

Best regards
Thomas


>
> Best regards
> Thomas
>
>>
>> In fact, through modifications in Patch v2, it allows only the 
>> selection of
>> DRM_VRAM_HELPER in the driver.
>> See the link below:
>> https://lore.kernel.org/all/20250729060728.82402-1-chuguangqing@inspur.com/T/#m3e33f8e155275ea548223c21777c191ecd392159 
>>
>>
>> Best regards
>> Chuguangqing
>>
>>> From: Thomas Zimmermann <tzimmermann@...e.de>
>>> To:chuguangqing <chuguangqing@...pur.com>; Maarten Lankhorst
>>> <maarten.lankhorst@...ux.intel.com>; Maxime Ripard 
>>> <mripard@...nel.org>;
>>> David Airlie <airlied@...il.com>; Simona Vetter <simona@...ll.ch>
>>> Cc: dri-devel@...ts.freedesktop.org; linux-kernel@...r.kernel.org
>>> Subject: Re: [PATCH 1/1] gpu: drm: fix compilation errors in 
>>> drm_vram_helper
>>>
>>> Hi
>>>
>>> Am 29.07.25 um 08:07 schrieb chuguangqing:
>>>> We encountered the following errors while compiling drm_vram_helper.ko
>>>>
>>>> ERROR: modpost: "drm_gem_ttm_print_info"
>>> [drivers/gpu/drm/drm_vram_helper.ko] undefined!
>>>> ERROR: modpost: "drm_gem_ttm_mmap"
>>> [drivers/gpu/drm/drm_vram_helper.ko] undefined!
>>>> The functions drm_gem_ttm_mmap and drm_gem_ttm_print_info are
>>> defined in drm_gem_ttm_helper.c. This patch adds 
>>> drm_gem_ttm_helper.o to
>>> DRM_VRAM_HELPER to resolve the undefined symbol errors.
>>>
>>> You need to select DRM_TTM_HELPER for your driver.
>>>
>>> Best regards
>>> Thomas
>>>
>>>> Signed-off-by: chuguangqing <chuguangqing@...pur.com>
>>>> ---
>>>>    drivers/gpu/drm/Makefile | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile index
>>>> 4dafbdc8f86a..abbe32ddf6d0 100644
>>>> --- a/drivers/gpu/drm/Makefile
>>>> +++ b/drivers/gpu/drm/Makefile
>>>> @@ -125,7 +125,7 @@ drm_suballoc_helper-y := drm_suballoc.o
>>>>    obj-$(CONFIG_DRM_SUBALLOC_HELPER) += drm_suballoc_helper.o
>>>>
>>>>    drm_vram_helper-y := drm_gem_vram_helper.o
>>>> -obj-$(CONFIG_DRM_VRAM_HELPER) += drm_vram_helper.o
>>>> +obj-$(CONFIG_DRM_VRAM_HELPER) += drm_vram_helper.o
>>>> +drm_gem_ttm_helper.o
>>>>
>>>>    drm_ttm_helper-y := drm_gem_ttm_helper.o
>>>>    drm_ttm_helper-$(CONFIG_DRM_FBDEV_EMULATION) +=
>>> drm_fbdev_ttm.o
>>>
>>> -- 
>>> -- 
>>> 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)