linux-kernel - Re: [PATCH net-next 1/4] net: mvneta: Convert to be 64 bits compatible

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Date:   Tue, 22 Nov 2016 22:04:12 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     Gregory CLEMENT <gregory.clement@...e-electrons.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Andrew Lunn <andrew@...n.ch>,
        Jason Cooper <jason@...edaemon.net>,
        Marcin Wojtas <mw@...ihalf.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH net-next 1/4] net: mvneta: Convert to be 64 bits compatible

On Tuesday, November 22, 2016 5:48:41 PM CET Gregory CLEMENT wrote:
> +#ifdef CONFIG_64BIT
> +       void *data_tmp;
> +
> +       /* In Neta HW only 32 bits data is supported, so in order to
> +        * obtain whole 64 bits address from RX descriptor, we store
> +        * the upper 32 bits when allocating buffer, and put it back
> +        * when using buffer cookie for accessing packet in memory.
> +        * Frags should be allocated from single 'memory' region,
> +        * hence common upper address half should be sufficient.
> +        */
> +       data_tmp = mvneta_frag_alloc(pp->frag_size);
> +       if (data_tmp) {
> +               pp->data_high = (u64)upper_32_bits((u64)data_tmp) << 32;
> +               mvneta_frag_free(pp->frag_size, data_tmp);
> +       }
> 

How does this work when the region spans a n*4GB address boundary?

	Arnd