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

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Message-ID: <BN8PR12MB3266A2F1F5F3F18F3A80BFC1D3870@BN8PR12MB3266.namprd12.prod.outlook.com>
Date:   Wed, 25 Sep 2019 11:41:04 +0000
From:   Jose Abreu <Jose.Abreu@...opsys.com>
To:     David Miller <davem@...emloft.net>,
        "Jose.Abreu@...opsys.com" <Jose.Abreu@...opsys.com>
CC:     "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "peppe.cavallaro@...com" <peppe.cavallaro@...com>,
        "alexandre.torgue@...com" <alexandre.torgue@...com>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "jonathanh@...dia.com" <jonathanh@...dia.com>,
        "bbiswas@...dia.com" <bbiswas@...dia.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: RE: [PATCH v3 0/2] net: stmmac: Enhanced addressing mode for DWMAC
 4.10

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.

---
Thanks,
Jose Miguel Abreu