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    SubjectRe: [PATCH 5.18 0309/1095] drm/panel: Fix build error when CONFIG_DRM_PANEL_SAMSUNG_ATNA33XC20=y && CONFIG_DRM_DISPLAY_HELPER=m
    On Wed, Aug 17, 2022 at 02:33:32PM -0700, Doug Anderson wrote:
    > Hi,
    >
    > On Mon, Aug 15, 2022 at 12:09 PM Greg Kroah-Hartman
    > <gregkh@linuxfoundation.org> wrote:
    > >
    > > From: Gao Chao <gaochao49@huawei.com>
    > >
    > > [ Upstream commit a67664860f7833015a683ea295f7c79ac2901332 ]
    > >
    > > If CONFIG_DRM_PANEL_SAMSUNG_ATNA33XC20=y && CONFIG_DRM_DISPLAY_HELPER=m,
    > > bulding fails:
    > >
    > > drivers/gpu/drm/panel/panel-samsung-atna33xc20.o: In function `atana33xc20_probe':
    > > panel-samsung-atna33xc20.c:(.text+0x744): undefined reference to
    > > `drm_panel_dp_aux_backlight'
    > > make: *** [vmlinux] Error 1
    > >
    > > Let CONFIG_DRM_PANEL_SAMSUNG_ATNA33XC20 select DRM_DISPLAY_DP_HELPER and
    > > CONFIG_DRM_DISPLAY_HELPER to fix this error.
    > >
    > > Fixes: 32ce3b320343 ("drm/panel: atna33xc20: Introduce the Samsung ATNA33XC20 panel")
    > > Reported-by: Hulk Robot <hulkci@huawei.com>
    > > Signed-off-by: Gao Chao <gaochao49@huawei.com>
    > > Reviewed-by: Douglas Anderson <dianders@chromium.org>
    > > Signed-off-by: Douglas Anderson <dianders@chromium.org>
    > > Link: https://patchwork.freedesktop.org/patch/msgid/20220524024551.539-1-gaochao49@huawei.com
    > > Signed-off-by: Sasha Levin <sashal@kernel.org>
    > > ---
    > > drivers/gpu/drm/panel/Kconfig | 2 ++
    > > 1 file changed, 2 insertions(+)
    >
    > While it doesn't hurt to land this patch as-is on 5.18 and older
    > kernels, it's not quite right. The symbols that this patch 'select'
    > don't actually exist on 5.18. ;-) Doing a `git grep` of
    > `DRM_DISPLAY_DP_HELPER` shows no hits except the one introduced in
    > this patch...
    >
    > If you want the equivalent fix for v5.18 and older, I believe you'd want:
    >
    > select DRM_DP_HELPER
    > select DRM_KMS_HELPER
    >
    > See commit 3755d35ee1d2 ("drm/panel: Select DRM_DP_HELPER for
    > DRM_PANEL_EDP") and commit 3c3384050d68 ("drm: Don't make
    > DRM_PANEL_BRIDGE dependent on DRM_KMS_HELPERS") which added those for
    > the (very similar) panel-edp.
    >
    > The first of those is what got changed in v5.19 in commit 1e0f66420b13
    > ("drm/display: Introduce a DRM display-helper module")
    >
    > So I guess the tl;dr:
    >
    > * If you leave this patch in 5.18 (and 5.15), nothing bad will happen
    > but the broken "randconfig" won't be fixed.
    >
    > * If you revert this patch in 5.18 (and 5.15) also nothing bad will
    > happen but also the broken "randconfig" won't be fixed.
    >
    > * If someone cares about the randconfig on 5.15 / 5.18, we need a
    > backport that adapts what's selected to the old symbol names.

    Thanks for letting us know, I'll leave it alone for now and see if
    anyone has problems.

    greg k-h

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