netdev - Re: ethernet/sfc/ warnings with 32-bit dma_addr

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Message-ID: <20200819145145.GA27058@infradead.org>
Date:   Wed, 19 Aug 2020 15:51:45 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Edward Cree <ecree@...arflare.com>
Cc:     Randy Dunlap <rdunlap@...radead.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Michael Brown <mbrown@...systems.co.uk>,
        Solarflare linux maintainers <linux-net-drivers@...arflare.com>,
        Martin Habets <mhabets@...arflare.com>
Subject: Re: ethernet/sfc/ warnings with 32-bit dma_addr_t

On Wed, Aug 19, 2020 at 11:37:00AM +0100, Edward Cree wrote:
> As far as I can tell, truncation to 32 bits is harmless ??? the
> ??called function (efx_init_io) already tries every mask from the
> ??passed one down to 32 bits in case of PCIe hardware limitations.

Which btw isn't needed.  These days dma_set_mask_and_coherent
and friends never fail because of a "too large" mask - it will
only fail in the rare case of a too small one.  So the two places
that set the dma mask could be simplified.