Re: [PATCH 42/43] drm/fbdev-generic: Convert to fbdev-ttm

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Hi

Am 22.10.24 um 15:31 schrieb Jon Hunter:
Hi Thomas,

On 12/03/2024 15:45, Thomas Zimmermann wrote:
Only TTM-based drivers use fbdev-generic. Rename it to fbdev-ttm and
change the symbol infix from _generic_ to _ttm_. Link the source file
into TTM helpers, so that it is only build if TTM-based drivers have
been selected. Select DRM_TTM_HELPER for loongson.

Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
---
  Documentation/gpu/drm-kms-helpers.rst         |  2 +-
  drivers/gpu/drm/Makefile                      |  5 +-
  drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c       |  6 +-
  .../{drm_fbdev_generic.c => drm_fbdev_ttm.c}  | 80 +++++++++----------
  .../gpu/drm/hisilicon/hibmc/hibmc_drm_drv.c   |  4 +-
  drivers/gpu/drm/loongson/Kconfig              |  1 +
  drivers/gpu/drm/loongson/lsdc_drv.c           |  4 +-
  drivers/gpu/drm/nouveau/nouveau_drm.c         |  6 +-
  drivers/gpu/drm/qxl/qxl_drv.c                 |  4 +-
  drivers/gpu/drm/tiny/bochs.c                  |  4 +-
  drivers/gpu/drm/vboxvideo/vbox_drv.c          |  4 +-
  drivers/gpu/drm/vmwgfx/vmwgfx_drv.c           |  4 +-
  include/drm/drm_fbdev_generic.h               | 15 ----
  include/drm/drm_fbdev_ttm.h                   | 15 ++++
  14 files changed, 77 insertions(+), 77 deletions(-)
  rename drivers/gpu/drm/{drm_fbdev_generic.c => drm_fbdev_ttm.c} (76%)
  delete mode 100644 include/drm/drm_fbdev_generic.h
  create mode 100644 include/drm/drm_fbdev_ttm.h

...

diff --git a/include/drm/drm_fbdev_ttm.h b/include/drm/drm_fbdev_ttm.h
new file mode 100644
index 0000000000000..9e6c3bdf35376
--- /dev/null
+++ b/include/drm/drm_fbdev_ttm.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: MIT */
+
+#ifndef DRM_FBDEV_TTM_H
+#define DRM_FBDEV_TTM_H
+
+struct drm_device;
+
+#ifdef CONFIG_DRM_FBDEV_EMULATION
+void drm_fbdev_ttm_setup(struct drm_device *dev, unsigned int preferred_bpp);
+#else
+static inline void drm_fbdev_ttm_setup(struct drm_device *dev, unsigned int preferred_bpp)
+{ }
+#endif
+
+#endif


I recently noticed that with Linux v6.11 it is possible to enable
CONFIG_DRM_FBDEV_EMULATION without enabling CONFIG_DRM_TTM_HELPER. Now
while this does not currently cause any build issues, I believe that if
the function drm_fbdev_ttm_setup() is ever used somewhere that does not
explicitly select CONFIG_DRM_TTM_HELPER, then you could get a 'ERROR:
modpost: "drm_fbdev_ttm_setup"'.

So I was thinking that may be this should be ...

diff --git a/include/drm/drm_fbdev_ttm.h b/include/drm/drm_fbdev_ttm.h
index 9e6c3bdf3537..5b6723a37caa 100644
--- a/include/drm/drm_fbdev_ttm.h
+++ b/include/drm/drm_fbdev_ttm.h
@@ -5,7 +5,7 @@

 struct drm_device;

-#ifdef CONFIG_DRM_FBDEV_EMULATION
+#if defined(CONFIG_DRM_FBDEV_EMULATION) && defined(CONFIG_DRM_TTM_HELPER)  void drm_fbdev_ttm_setup(struct drm_device *dev, unsigned int preferred_bpp);
 #else
 static inline void drm_fbdev_ttm_setup(struct drm_device *dev, unsigned int preferred_bpp)


The above function has been removed now in -next, but I believe we could
have the same problem with drm_fbdev_ttm_helper_fb_probe()?

We'd turn a linker/modpost error into a compiler error. Likely makes no difference. And AFAICT every driver that selects TTM also selects TTM_HELPER. Drivers without TTM should not use this header.

(DRM_TTM and DRM_TTM_HELPER are separate config options for historical reasons. Maybe one of them could go away.)

Best regards
Thomas


Cheers
Jon


--
--
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)




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