netdev - RE: [PATCH] net: davinci_emac: Add pre_open, post

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Message-ID: <B5906170F1614E41A8A28DE3B8D121433EA72820@DBDE01.ent.ti.com>
Date:	Thu, 3 May 2012 10:44:44 +0000
From:	"Bedia, Vaibhav" <vaibhav.bedia@...com>
To:	"Mark A. Greer" <mgreer@...malcreek.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH] net: davinci_emac: Add pre_open, post_stop platform
 callbacks

On Thu, May 03, 2012 at 05:17:18, Mark A. Greer wrote:
> From: "Mark A. Greer" <mgreer@...malcreek.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.

Regards,
Vaibhav
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