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SubjectRe: [PATCH v6 16/36] nds32: DMA mapping API
Hi, Arnd:

2018-01-23 16:23 GMT+08:00 Greentime Hu <green.hu@gmail.com>:
> Hi, Arnd:
>
> 2018-01-18 18:26 GMT+08:00 Arnd Bergmann <arnd@arndb.de>:
>> On Mon, Jan 15, 2018 at 6:53 AM, Greentime Hu <green.hu@gmail.com> wrote:
>>> From: Greentime Hu <greentime@andestech.com>
>>>
>>> This patch adds support for the DMA mapping API. It uses dma_map_ops for
>>> flexibility.
>>>
>>> Signed-off-by: Vincent Chen <vincentc@andestech.com>
>>> Signed-off-by: Greentime Hu <greentime@andestech.com>
>>
>> I'm still unhappy about the way the cache flushes are done here as discussed
>> before. It's not a show-stopped, but no Ack from me.
>
> How about this implementation?
>
> static void
> nds32_dma_sync_single_for_cpu(struct device *dev, dma_addr_t handle,
> size_t size, enum dma_data_direction dir)
> {
> switch (direction) {
> case DMA_TO_DEVICE: /* writeback only */
> break;
> case DMA_FROM_DEVICE: /* invalidate only */
> case DMA_BIDIRECTIONAL: /* writeback and invalidate */
> cpu_dma_inval_range(start, end);
> break;
> default:
> BUG();
> }
> }
>
> static void
> nds32_dma_sync_single_for_device(struct device *dev, dma_addr_t handle,
> size_t size, enum dma_data_direction dir)
> {
> switch (direction) {
> case DMA_FROM_DEVICE: /* invalidate only */
> break;
> case DMA_TO_DEVICE: /* writeback only */
> case DMA_BIDIRECTIONAL: /* writeback and invalidate */
> cpu_dma_wb_range(start, end);
> break;
> default:
> BUG();
> }
> }

I am not sure if I understand it correctly.
I list all the combinations.

RAM to DEVICE
before DMA => writeback cache
after DMA => nop

DEVICE to RAM
before DMA => nop
after DMA => invalidate cache

static void consistent_sync(void *vaddr, size_t size, int direction, int master)
{
unsigned long start = (unsigned long)vaddr;
unsigned long end = start + size;

if (master == FOR_CPU) {
switch (direction) {
case DMA_TO_DEVICE:
break;
case DMA_FROM_DEVICE:
case DMA_BIDIRECTIONAL:
cpu_dma_inval_range(start, end);
break;
default:
BUG();
}
} else {
/* FOR_DEVICE */
switch (direction) {
case DMA_FROM_DEVICE:
break;
case DMA_TO_DEVICE:
case DMA_BIDIRECTIONAL:
cpu_dma_wb_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 *)phys_to_virt(handle), size, dir, FOR_CPU);
}

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 *)phys_to_virt(handle), size, dir, FOR_DEVICE);
}

static dma_addr_t nds32_dma_map_page(struct device *dev, struct page *page,
unsigned long offset, size_t size,
enum dma_data_direction dir,
unsigned long attrs)
{
if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
consistent_sync((void *)(page_address(page) + offset),
size, dir, FOR_DEVICE);
return page_to_phys(page) + offset;
}

static void nds32_dma_unmap_page(struct device *dev, dma_addr_t handle,
size_t size, enum dma_data_direction dir,
unsigned long attrs)
{
if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
consistent_sync(phys_to_virt(handle), size, dir, FOR_CPU);
}

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