netdev - Re: [PATCH v3 0/2] net: stmmac: Enhanced addressing mode for DWMAC 4.10

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Date:   Wed, 25 Sep 2019 14:01:22 +0200 (CEST)
From:   David Miller <davem@...emloft.net>
To:     Jose.Abreu@...opsys.com
Cc:     thierry.reding@...il.com, peppe.cavallaro@...com,
        alexandre.torgue@...com, f.fainelli@...il.com,
        jonathanh@...dia.com, bbiswas@...dia.com, netdev@...r.kernel.org,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH v3 0/2] net: stmmac: Enhanced addressing mode for DWMAC
 4.10

From: Jose Abreu <Jose.Abreu@...opsys.com>
Date: Wed, 25 Sep 2019 11:41:04 +0000

> From: David Miller <davem@...emloft.net>
> Date: Sep/25/2019, 12:33:53 (UTC+00:00)
> 
>> From: Jose Abreu <Jose.Abreu@...opsys.com>
>> Date: Wed, 25 Sep 2019 10:44:53 +0000
>> 
>> > From: David Miller <davem@...emloft.net>
>> > Date: Sep/24/2019, 20:45:08 (UTC+00:00)
>> > 
>> >> From: Thierry Reding <thierry.reding@...il.com>
>> >> Date: Fri, 20 Sep 2019 19:00:34 +0200
>> >> 
>> >> Also, you're now writing to the high 32-bits unconditionally, even when
>> >> it will always be zero because of 32-bit addressing.  That looks like
>> >> a step backwards to me.
>> > 
>> > Don't agree. As per previous discussions and as per my IP knowledge, if 
>> > EAME is not enabled / not supported the register can still be written. 
>> > This is not fast path and will not impact any remaining operation. Can 
>> > you please explain what exactly is the concern about this ?
>> > 
>> > Anyway, this is an important feature for performance so I hope Thierry 
>> > re-submits this once -next opens and addressing the review comments.
>> 
>> Perhaps I misunderstand the context, isn't this code writing the
>> descriptors for every packet?
> 
> No, its just setting up the base address for the descriptors which is 
> done in open(). The one that's in the fast path is the tail address, 
> which is always the lower 32 bits.

Aha, ok, yes then initializing both parts unconditionally is fine.