linux-kernel - Re: [PATCH V8 1/5] dma-mapping: Rework dma_get_cache

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Date:   Wed, 18 Oct 2017 10:23:36 -0700
From:   Mark Greer <mgreer@...malcreek.com>
To:     Huacai Chen <chenhc@...ote.com>
Cc:     Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Fuxin Zhang <zhangfx@...ote.com>, linux-kernel@...r.kernel.org,
        Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <james.hogan@...tec.com>,
        linux-mips@...ux-mips.org,
        "James E . J . Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, Tejun Heo <tj@...nel.org>,
        linux-ide@...r.kernel.org, stable@...r.kernel.org,
        "Michael S . Tsirkin" <mst@...lanox.co.il>,
        Pawel Osciak <pawel@...iak.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Michael Chan <michael.chan@...adcom.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Ivan Mikhaylov <ivan@...ibm.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Andy Gross <agross@...eaurora.org>,
        "Mark A . Greer" <mgreer@...malcreek.com>,
        Robert Baldyga <r.baldyga@...kerion.com>
Subject: Re: [PATCH V8 1/5] dma-mapping: Rework dma_get_cache_alignment()

On Tue, Oct 17, 2017 at 04:05:38PM +0800, Huacai Chen wrote:
> Make dma_get_cache_alignment() to accept a 'dev' argument. As a result,
> it can return different alignments due to different devices' I/O cache
> coherency.
> 
> Currently, ARM/ARM64 and MIPS support coherent & noncoherent devices
> co-exist. This may be extended in the future, so add a new function
> pointer (i.e, get_cache_alignment) in 'struct dma_map_ops' as a generic
> solution.

Hi Huacai.

> diff --git a/drivers/tty/serial/mpsc.c b/drivers/tty/serial/mpsc.c
> index 67ffecc..c708457 100644
> --- a/drivers/tty/serial/mpsc.c
> +++ b/drivers/tty/serial/mpsc.c
> @@ -81,19 +81,19 @@
>   * Number of Tx & Rx descriptors must be powers of 2.
>   */
>  #define	MPSC_RXR_ENTRIES	32
> -#define	MPSC_RXRE_SIZE		dma_get_cache_alignment()
> +#define	MPSC_RXRE_SIZE		dma_get_cache_alignment(dma_dev)

I would much prefer that you add a parameter to the macro to avoid forcing
a non-flexible and non-obvious variable definition wherever it is used.
What I mean is something like:

#define MPSC_RXRE_SIZE(d)		dma_get_cache_alignment(d)

Similarly for all of the other macros and where they're used.

Thanks,

Mark
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