Hi
Am 09.12.25 um 09:22 schrieb Helge Deller:
On 12/9/25 08:27, Thomas Zimmermann wrote:
Hi
Am 09.12.25 um 05:27 schrieb Chintan Patel:
Hi all,
This small series makes several legacy fbdev drivers buildable with
CONFIG_FB_DEVICE=n. Currently, multiple fbdev drivers rely on
fb_info->dev
and sysfs attribute registration unconditionally, which leads to build
failures whenever FB_DEVICE is disabled.
Thomas previously noted that FB_DEVICE should eventually become
optional
and that drivers should not depend on sysfs or fb_info->dev being
present
unless the Kconfig explicitly selects it. This series pushes in that
direction by tightening the FB_DEVICE dependency boundary without
changing
any runtime behaviour when FB_DEVICE=y.
What this series does *not* change
- No functional behaviour changes when FB_DEVICE=y.
- No removal of sysfs interfaces.
- No changes to fbops, memory allocation, or display update paths.
Build & test coverage
Tested with the following combinations:
1. **FB=y, FB_DEVICE=y**
- Baseline configuration; no regressions expected.
2. **FB=y, FB_DEVICE=n**
- Drivers build successfully.
- No sysfs attributes are created.
- fbdev devices operate normally (where applicable).
3. **FB=n**
- Drivers depend on FB, so they properly do not build, unchanged.
Motivation
This moves fbdev closer to supporting FB_DEVICE as truly optional,
helps
reduce Kconfig entanglement, and clears several long-standing TODO
items
as suggested by Thomas Zimmermann around legacy sysfs usage inside
fbdev
drivers.
Feedback is welcome, especially on whether the guard boundaries around
sysfs are placed correctly or whether more logic should be pulled under
CONFIG_FB_DEVICE.
I left a comment on the first patch. If things still build nicely, then
Acked-by: Thomas Zimmermann <[email protected]>
for the series.
This whole series adds a whole lot of ifdef'ery, which I think is the
worst approach. It makes the code less readable and leads to two code
paths, which may trigger different build errors depending on the config.
I'm sure it must be possible to do the same without adding more #ifdefs,
e.g. by introducing a function like dev_of_fbinfo(fbinfo) which
simply returns NULL for the FB_DEVICE=n case. Then, that value can be
tested
like
if (dev_of_fbinfo(fbinfo))
{...do-the-things...}
For the FB_DEVICE=n case this will then be optimized out by the compiler,
while you still have full compiler syntax checking.
Thoughts?
Your choice. I don't see this as an important fix. The FB_DEVICE=n case
is mostly useful for DRM-based systems that do not want to expose fbdev
interfaces to user space. Those are the vast majority today. The very
few special builds with fbdev drivers would likely use FB_DEVICE=y anyway.
Best regards
Thomas
Helge
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)
