linux-kernel - Re: allow larger than require DMA masks

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Message-ID: <20190924212554.GA31357@lst.de>
Date:   Tue, 24 Sep 2019 23:25:54 +0200
From:   Christoph Hellwig <hch@....de>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     Sven Schnelle <svens@...ckframe.org>,
        Christoph Hellwig <hch@....de>, Helge Deller <deller@....de>,
        linux-parisc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: allow larger than require DMA masks

On Mon, Sep 23, 2019 at 08:59:42PM -0400, James Bottomley wrote:
> > 	if (mask > ~0U)
> > »     »       return 0;
> > 
> > Removing the if() makes the DMA mapping work. It's almost midnight
> > here, so i won't look into that any further today. Does anyone have
> > an opinion on this behaviour? Otherwise i will look a bit more into
> > this in the next days.
> 
> The reason for the if was to kick the device into 32 bit descriptors,
> which are usually more efficient, especially with older dual descriptor
> format cards like we have on parisc systems.

These days we use the dma_get_required_mask API to query for that.

Svens patch looks right for how we are now using the DMA mask setting
API.