linux-kernel - Re: [PATCH v8 4/4] drivers: net: Add APM X-Gene SoC ethernet driver support.

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Message-ID: <CAKh23FnraikR3apUtrxOWYransQYEFVVJcSaL9d6OWzeWiVT1A@mail.gmail.com>
Date:	Wed, 9 Jul 2014 15:38:00 -0700
From:	Iyappan Subramanian <isubramanian@....com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"jcm@...hat.com" <jcm@...hat.com>, patches <patches@....com>,
	Ravi Patel <rapatel@....com>, Keyur Chudgar <kchudgar@....com>
Subject: Re: [PATCH v8 4/4] drivers: net: Add APM X-Gene SoC ethernet driver support.

On Tue, Jun 24, 2014 at 10:34 PM, David Miller <davem@...emloft.net> wrote:
> From: Iyappan Subramanian <isubramanian@....com>
> Date: Fri, 20 Jun 2014 16:18:16 -0700
>
>> This patch adds network driver for APM X-Gene SoC ethernet.
>>
>> Signed-off-by: Iyappan Subramanian <isubramanian@....com>
>> Signed-off-by: Ravi Patel <rapatel@....com>
>> Signed-off-by: Keyur Chudgar <kchudgar@....com>
>
> I really don't like how you handle the hardware descriptors in this
> driver.
>
> You copy back and forth between a software format and the hardware
> format.  That's extremely wasteful and will hurt performance.
>
> Just use the raw format throughout, you can extract the fields when
> you need them.

I agree and I will fix this and resubmit the patches.

>
> You also make two passes when building a hardware descriptor:
>
> 1) write the values
> 2) endian swap
>
> This means you make three memory accesses on every 64-bit word
> in every descriptor you setup, this is really inefficient.
>
> You should just byte swap them in-situ as you build the raw
> descriptors.
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