On Mon, 31 Dec 2018, Finn Thain wrote:

On Sun, 30 Dec 2018, James Bottomley wrote:

quoted

That said, as has been pointed out, the current #ifdef has a failing 
corner case when both are modular (because the code should then be 
included).  The runtime macro that correctly expresses this is 
IS_REACHABLE(CONFIG_NVRAM).

No, in the case of CONFIG_NVRAM=m, the conditional code is deliberately 
excluded. This is discussed in the patch description. The convention on 
PPC32 is that device drivers drop support for NVRAM in this situation. 

I've adopted the PPC32 convention here because M68K drivers and PPC32 
drivers have to co-exist (I'm thinking of valkyriefb, but there are other 
examples).

I agree with your comment in principle, that these drivers should be using 
IS_REACHABLE(CONFIG_NVRAM), not defined(CONFIG_NVRAM).

$ grep -lrw CONFIG_NVRAM drivers/
drivers/video/fbdev/matrox/matroxfb_base.c
drivers/video/fbdev/platinumfb.c
drivers/video/fbdev/controlfb.c
drivers/video/fbdev/valkyriefb.c
drivers/video/fbdev/imsttfb.c
drivers/scsi/atari_scsi.c
$ 

But I think this is not the fault of this patch; it's just a historical 
accident.

Having said that, I will rework this series to convert all of the above 
drivers to IS_REACHABLE(CONFIG_NVRAM). I think it would be an improvement.

Besides, it seems likely that some rework involving ppc_md will be needed 
too because as Arnd pointed out, it would be good to avoid two sets of 
nvram accessor methods.

--