On Mon, 31 Dec 2018, Arnd Bergmann wrote: > On Sun, Dec 30, 2018 at 4:29 AM Finn Thain <fth...@telegraphics.com.au> wrote: > > > > On Sat, 29 Dec 2018, Arnd Bergmann wrote: > > > > > On Wed, Dec 26, 2018 at 1:43 AM Finn Thain <fth...@telegraphics.com.au> > > > wrote: > > > > > > > +static ssize_t ppc_nvram_get_size(void) > > > > +{ > > > > + if (ppc_md.nvram_size) > > > > + return ppc_md.nvram_size(); > > > > + return -ENODEV; > > > > +} > > > > > > > +const struct nvram_ops arch_nvram_ops = { > > > > + .read = ppc_nvram_read, > > > > + .write = ppc_nvram_write, > > > > + .get_size = ppc_nvram_get_size, > > > > + .sync = ppc_nvram_sync, > > > > +}; > > > > > > Coming back to this after my comment on the m68k side, I notice that > > > there is now a double indirection through function pointers. Have > > > you considered completely removing the operations from ppc_md > > > instead by having multiple copies of nvram_ops? > > > > > > > I considered a few alternatives. I figured that it was refactoring > > that could be deferred, as it would be confined to arch/powerpc. I was > > more interested in the cross-platform API. > > Fair enough. > > > > With the current method, it does seem odd to have a single > > > per-architecture instance of the exported structure containing > > > function pointers. This doesn't give us the flexibility of having > > > multiple copies in the kernel the way that ppc_md does, but it adds > > > overhead compared to simply exporting the functions directly. > > > > > > > You're right, there is overhead here. > > > > With a bit of auditing, wrappers like the one you quoted (which merely > > checks whether or not a ppc_md method is implemented) could surely be > > avoided. > > > > The arch_nvram_ops methods are supposed to optional (that is, they are > > allowed to be NULL). > > > > We could call exactly the same function pointers though either ppc_md > > or arch_nvram_ops. That would avoid the double indirection. > > I think you can have a 'const' structure in the __ro_after_init section, > so without changing anything else, powerpc could just copy the function > pointers from ppc_md into the arch_nvram_ops at early init time, which > should ideally simplify your implementation as well. >
This "early init time" could be hard to pin down... It has to be after ppc_md methods are initialized but before the nvram_ops methods get used (e.g. by the framebuffer console). Seems a bit fragile (?) Your suggestion to completely remove the ppc_md.nvram* methods might be a better way. It just means functions get assigned to nvram_ops pointers instead of ppc_md pointers. The patch is simple enough, but it assumes that arch_nvram_ops is not const. The struct machdep_calls ppc_md is not const, so should we worry about dropping the const for the struct nvram_ops arch_nvram_ops? -- > Arnd >