On Mon, 31 Dec 2018, Arnd Bergmann wrote:
On Sun, Dec 30, 2018 at 4:29 AM Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx> wrote:
On Sat, 29 Dec 2018, Arnd Bergmann wrote:
On Wed, Dec 26, 2018 at 1:43 AM Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx> 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
