[PATCH] net: davinci_emac: Add pre_open, post_stop platform callbacks

"Bedia, Vaibhav" [off-list ref] writes:

On Thu, May 03, 2012 at 05:17:18, Mark A. Greer wrote:

quoted

From: "Mark A. Greer" <mgreer@animalcreek.com>

The davinci EMAC driver has been incorporated into the am35x
family of SoC's which is OMAP-based.  The incorporation is
incomplete in that the EMAC cannot unblock the [ARM] core if
its blocked on a 'wfi' instruction.  This is an issue with
the cpu_idle code because it has the core execute a 'wfi'
instruction.

To work around this issue, add platform data callbacks which
are called at the beginning of the open routine and at the
end of the stop routine of the davinci_emac driver.  The
callbacks allow the platform code to issue disable_hlt() and
enable_hlt() calls appropriately.  Calling disable_hlt()
prevents cpu_idle from issuing the 'wfi' instruction.

It is not sufficient to simply call disable_hlt() when
there is an EMAC present because it could be present but
not actually used in which case, we do want the 'wfi' to
be executed.

Are you trying to say that if ARM executes _just_ wfi and _absolutely
nothing else_ is done in the OMAP PM code, EMAC stops working?

However, if this is indeed the case, then probably a better solution would be
to invoke disable_hlt() from the board file when EMAC support is compiled in.

No.  As Mark stated in the changelog, doing that will prevent any
low-power states states even if the EMAC is not in use.  IMO, it is best
to only prevent WFI when absolutely needed.

Kevin