linux-kernel - Re: [PATCH 13/31] nds32: DMA mapping API

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Date:   Thu, 9 Nov 2017 15:12:05 +0800
From:   Greentime Hu <green.hu@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Greentime <greentime@...estech.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Networking <netdev@...r.kernel.org>,
        Vincent Chen <vincentc@...estech.com>, deanbo422@...il.com
Subject: Re: [PATCH 13/31] nds32: DMA mapping API

2017-11-08 17:09 GMT+08:00 Arnd Bergmann <arnd@...db.de>:
> On Wed, Nov 8, 2017 at 6:55 AM, Greentime Hu <green.hu@...il.com> wrote:
>
>> +static void consistent_sync(void *vaddr, size_t size, int direction)
>> +{
>> +       unsigned long start = (unsigned long)vaddr;
>> +       unsigned long end = start + size;
>> +
>> +       switch (direction) {
>> +       case DMA_FROM_DEVICE:   /* invalidate only */
>> +               cpu_dma_inval_range(start, end);
>> +               break;
>> +       case DMA_TO_DEVICE:     /* writeback only */
>> +               cpu_dma_wb_range(start, end);
>> +               break;
>> +       case DMA_BIDIRECTIONAL: /* writeback and invalidate */
>> +               cpu_dma_wbinval_range(start, end);
>> +               break;
>> +       default:
>> +               BUG();
>> +       }
>> +}
>
>> +
>> +static void
>> +nds32_dma_sync_single_for_cpu(struct device *dev, dma_addr_t handle,
>> +                             size_t size, enum dma_data_direction dir)
>> +{
>> +       consistent_sync((void *)dma_to_virt(dev, handle), size, dir);
>> +}
>> +
>> +static void
>> +nds32_dma_sync_single_for_device(struct device *dev, dma_addr_t handle,
>> +                                size_t size, enum dma_data_direction dir)
>> +{
>> +       consistent_sync((void *)dma_to_virt(dev, handle), size, dir);
>> +}
>
> You do the same cache operations for _to_cpu and _to_device, which
> usually works,
> but is more expensive than you need. It's better to take the ownership into
> account and only do what you need.
>

Thanks.

Like this?

static void
nds32_dma_sync_single_for_cpu(struct device *dev, dma_addr_t handle,
                              size_t size, enum dma_data_direction dir)
{
        consistent_sync((void *)dma_to_virt(dev, handle), size,
DMA_FROM_DEVICE);
}

static void
nds32_dma_sync_single_for_device(struct device *dev, dma_addr_t handle,
                                 size_t size, enum dma_data_direction dir)
{
        consistent_sync((void *)dma_to_virt(dev, handle), size,
DMA_TO_DEVICE);
}