Re: [RFC PATCH 05/17] phy_driver: Make .read_status()/.config_aneg() optional

From: Mike Frysinger
Date: Tue Oct 25 2011 - 03:06:36 EST

On Fri, Oct 21, 2011 at 01:13, Kyle Moffett wrote:
> On Thu, Oct 20, 2011 at 17:14, Mike Frysinger wrote:
>> On Thursday 20 October 2011 17:10:12 Mike Frysinger wrote:
>>> On Thursday 20 October 2011 17:00:12 Kyle Moffett wrote:
>>> > Approximately 90% of the PHY drivers follow the PHY layer docs and
>>> > simply use &genphy_read_status and &genphy_config_aneg.  There would
>>> > seem to be little point in requiring them all to manually specify those
>>> > functions.
>>> well, it does make sense if you think about the compile vs build time
>>> overhead.  yes, your patch does make things much nicer to read, and a
>>> little easier to maintain the source.  however, it adds runtime overhead
>>> (checking the func pointers) while the func pointer storage is unchanged
>>> (it's now a NULL pointer instead of pointing to the genphy funcs).
>>> personally, i think the savings in runtime and smaller compiled code is
>>> more important.  so i'm going to NAK this.  sorry.
>> ah, sorry, i was thinking this was u-boot since we were just having
>> conversations there.
>> since this is Linux, and i don't have real standing in the general netdev
>> community, i can't really NAK here.  but i think my comment still stands in
>> that this patch makes things much worse than the minor code style improvement.
> I would argue that the PHY layer itself is not remotely a hot-path,
> especially not to the level of caring about an extra if statement.  A
> single phy_read() is a sleeping call which goes over a slow serial
> bus, so code maintainability is much more important.

i disagree. ignoring that, what you ultimately desire can be
accomplished without bloating the kernel.

option 1: this can be done in the registration func just like the mtd
layer. if (!func_pointer) func_pointer = default;

option 2: introduce a new macro in the common phy header similar to:
.config_aneg = genphy_config_aneg, \
.read_status = genphy_read_status
and then use that in the phy_driver init structs:
struct phy_driver bcm5411_driver = {
.config_aneg = bcm5411_config_aneg,

however, imo, these func pointer arrays really should be in the
.rodata section with proper const markers. this would require
breaking out into a new phy_driver_opts struct since the phy_driver
struct has read/write fields (like the list structure). option 2
should allow this to work.
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