On 20/02/18 12:34, Thierry Reding wrote: > On Mon, Feb 19, 2018 at 11:59:23PM +0100, Daniel Vetter wrote: >> On Mon, Feb 19, 2018 at 10:06:22PM +0200, Jyri Sarha wrote: >>> Currently there is no way for a master drm driver to protect against an >>> attached panel driver from being unloaded while it is in use. The >>> least we can do is to indicate the usage by incrementing the module >>> reference count. >>> >>> Signed-off-by: Jyri Sarha <jsarha@xxxxxx> >>> cc: eric@xxxxxxxxxx >>> cc: laurent.pinchart@xxxxxxxxxxxxxxxx >>> --- >>> I do not see any module_get/put code in drm core. Is there is a reason >>> for that? >>> >>> There is two more alternative places for adding the module_get/put >>> code. One is puting it directly to drm_panel_attach() and >>> drm_panel_detach(). However, if the same module implements both the >>> master drm driver and the panel (like tilcdc does with its >>> tilcdc_panel.c), then attaching the panel will lock the module in for >>> no good reason. Still, this solution should work with drm bridges as I >>> do not see any reason why anybody would implement bridge drivers in >>> the same module with the master drm driver. >>> >>> The other place to put the code would in the master drm driver. But >>> for handling the situation with bridges would need the device pointer >>> in struct drm_bridge. >> >> I think this looks like a reasonable place to do this. Looking at the code >> we seem to have a similar issue with the bridge driver itself. I think >> we need to wire through the module owner stuff and add a try_modeul_get to >> of_drm_find_bridge (and any other helper used to find bridge instances). > > I disagree. module_get() is only going to protect you from unloading a > module that's in use, but there are other ways to unbind a driver from > the device and cause subsequent mayhem. > Yes. This is not a full fix for the issue. But AFAIK at the moment there is no infrastructure to tear down the whole drm device grace fully when a bridge driver or panel is removed. So this should be considered as a partial remedy protecting user from accidentally crashing the drm driver by unloading the wrong module first. That is why I wrote "least we can do". > struct device_link was "recently" introduced to fix that issue. > Unfortunately I do not have time to do full fix for the issue, but in any case I think this patch is a step to the right direction. The module reference count should anyway be increased at least to know that the driver code remains in memory, even if the device is not there any more. Then again the display panels or bridges are hardly ever hot pluggable devices, so they do not normally vanish just like that, unless someone is being nasty and forcibly unbinding them. But yes, I know that is a bad excuse for broken behaviour. Best regards, Jyri -- Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
