netdev - RE: [PATCH 1/2] ibm_newemac: Add Support for MAL Interrupt Coalescing

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Date:	Mon, 21 Sep 2009 17:53:44 -0700
From:	"Prodyut Hazarika" <phazarika@...c.com>
To:	"Benjamin Herrenschmidt" <benh@...nel.crashing.org>,
	"prodyut hazarika" <prodyuth@...il.com>
Cc:	<netdev@...r.kernel.org>, "Feng Kan" <fkan@...c.com>,
	"Loc Ho" <lho@...c.com>, "Victor Gallardo" <vgallardo@...c.com>,
	<bhutchings@...arflare.com>, <linuxppc-dev@...ts.ozlabs.org>,
	<davem@...emloft.net>, <jwboyer@...ux.vnet.ibm.com>,
	<lada.podivin@...il.com>
Subject: RE: [PATCH 1/2] ibm_newemac: Add Support for MAL Interrupt Coalescing

Hi Ben,

> Well... the above is a HW limitation :-) IE. I was suggesting you fix
> the HW, but in the case where you already did and the current MAL in
> your SoC can indeed mask the interrupt per-channel, then that's great
> and we should definitely look into having the driver go back to a more
> standard NAPI model on MALs that have that capability.

In the newer revs of 460EX/GT and 405EX, we have Interrupt coalescing
both on Tx and Rx per channel (physical not virtual), which can be
enabled/disabled per channel via UIC. The Tx/Rx Coalesce mappings are
defined in the dts file. But in the older revs, there is only a global
EOP_Int_Enable in the MAL configuration register. There can be a
possible way even for older SoCs if we use the MAL descriptor I bit and
not the global EOP_Int_Enable. But to turn on/off the channel, we will
have to go and set/clear the I bit in whole of MAL descriptor ring for
that channel. That might be really inefficient.

What would you suggest?

Thanks
Prodyut

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