Re: [PATCH] RISC-V: KVM: fixup undefined reference to riscv_cbom_block_size

[Conor Dooley <conor.dooley@microchip.com>]

On Mon, Oct 10, 2022 at 08:59:49AM +0200, Andrew Jones wrote:
> On Mon, Oct 10, 2022 at 07:42:04AM +0100, Conor Dooley wrote:
> > On Mon, Oct 10, 2022 at 09:33:29AM +0800, Vernon Yang wrote:
> > > When some RISC-V compilers do not support the Zicbom extension,
> > > the build system auto disable the CONFIG_RISCV_ISA_ZICBOM, so the
> > > source code of the relevant function is not compiled, resulting
> > > in the definition of the riscv_cbom_block_size variable cannot
> > > be found
> > 
> > Hmm, my understanding was that riscv_cbom_block_size was not supposed to
> > depend on CONFIG_RISCV_ISA_ZICBOM because the thead is able to use it
> > even if the toolchain does not support it.
> > 
> > The code in cacheflush.h looks like:
> > extern unsigned int riscv_cbom_block_size;
> > #ifdef CONFIG_RISCV_ISA_ZICBOM
> > void riscv_init_cbom_blocksize(void);
> > #else
> > static inline void riscv_init_cbom_blocksize(void) { }
> > #endif
> > 
> > #ifdef CONFIG_RISCV_DMA_NONCOHERENT
> > void riscv_noncoherent_supported(void);
> > #endif
> > 
> > It's early and I only had a quick look but I think that this is not
> > defined because RISCV_DMA_NONCOHERENT is not defined, not because of
> > RISCV_ISA_ZICBOM.
> 
> thead is able to use riscv_cbom_block_size because it does its own
> initialization of it and selects RISCV_DMA_NONCOHERENT to get access
> to it. KVM depends on the initializer in dma-noncoherent.c, which is
> guarded by RISCV_ISA_ZICBOM and does not select RISCV_DMA_NONCOHERENT,
> but RISCV_ISA_ZICBOM does. I think guarding use of riscv_cbom_block_size
> with RISCV_ISA_ZICBOM in KVM makes sense.

Aight chief, you know the code better than I do :)

> > I'm not the KVM maintainer, but I dislike #ifdefery
> > in c files, so it'd be nice I think to sort this out in the header and
> > not have to worry about guarding the variable.
> 
> I also dislike #ifdefery, but unless we move riscv_cbom_block_size to
> an unconditionally built file like cacheflush.c (as Anup once did), then
> we don't have much choice.

Fair enough. Maybe once fixes, for-next & some of Heiko's cleanups have
aligned it'll make sense to do such a change.

Sorry for the noise then,
Conor.