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SubjectRe: [PATCH 1/2] dma-coherent: Add one parameter to save available coherent memory
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On 31/05/18 06:55, Baolin Wang wrote:
> It is incorrect to use mem->size to valid if there are enough coherent
> memory to allocate in __dma_alloc_from_coherent(), since some devices
> may mark some occupied coherent memory by dma_mark_declared_memory_occupied().
>
> So we can introduce one 'avail' parameter to save the available device
> coherent memory, to valid if we have enough coherent memory for the device
> to allocate.

We already have dma_mem->size stored for other reasons, so there's
little harm in using it for a rough sanity check to short-circuit the
odd allocation which cannot possibly succeed, but adding machinery
purely for the sake an ever-so-slightly more accurate, but still far
from exhaustive, check doesn't really seem worth it.

Even if size <= dma_mem->avail there's still no guarantee that the
allocation will actually succeed, so what benefit does the explicit
accounting provide?

Robin.

> Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
> ---
> drivers/base/dma-coherent.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c
> index 597d408..ce19832 100644
> --- a/drivers/base/dma-coherent.c
> +++ b/drivers/base/dma-coherent.c
> @@ -18,6 +18,7 @@ struct dma_coherent_mem {
> unsigned long *bitmap;
> spinlock_t spinlock;
> bool use_dev_dma_pfn_offset;
> + int avail;
> };
>
> static struct dma_coherent_mem *dma_coherent_default_memory __ro_after_init;
> @@ -73,6 +74,7 @@ static int dma_init_coherent_memory(
> dma_mem->device_base = device_addr;
> dma_mem->pfn_base = PFN_DOWN(phys_addr);
> dma_mem->size = pages;
> + dma_mem->avail = pages;
> dma_mem->flags = flags;
> spin_lock_init(&dma_mem->spinlock);
>
> @@ -141,6 +143,7 @@ void *dma_mark_declared_memory_occupied(struct device *dev,
> dma_addr_t device_addr, size_t size)
> {
> struct dma_coherent_mem *mem = dev->dma_mem;
> + int order = get_order(size);
> unsigned long flags;
> int pos, err;
>
> @@ -151,7 +154,9 @@ void *dma_mark_declared_memory_occupied(struct device *dev,
>
> spin_lock_irqsave(&mem->spinlock, flags);
> pos = PFN_DOWN(device_addr - dma_get_device_base(dev, mem));
> - err = bitmap_allocate_region(mem->bitmap, pos, get_order(size));
> + err = bitmap_allocate_region(mem->bitmap, pos, order);
> + if (!err)
> + mem->avail -= 1 << order;
> spin_unlock_irqrestore(&mem->spinlock, flags);
>
> if (err != 0)
> @@ -170,7 +175,7 @@ static void *__dma_alloc_from_coherent(struct dma_coherent_mem *mem,
>
> spin_lock_irqsave(&mem->spinlock, flags);
>
> - if (unlikely(size > (mem->size << PAGE_SHIFT)))
> + if (unlikely(size > (mem->avail << PAGE_SHIFT)))
> goto err;
>
> pageno = bitmap_find_free_region(mem->bitmap, mem->size, order);
> @@ -182,6 +187,7 @@ static void *__dma_alloc_from_coherent(struct dma_coherent_mem *mem,
> */
> *dma_handle = mem->device_base + (pageno << PAGE_SHIFT);
> ret = mem->virt_base + (pageno << PAGE_SHIFT);
> + mem->avail -= 1 << order;
> spin_unlock_irqrestore(&mem->spinlock, flags);
> memset(ret, 0, size);
> return ret;
> @@ -244,6 +250,7 @@ static int __dma_release_from_coherent(struct dma_coherent_mem *mem,
>
> spin_lock_irqsave(&mem->spinlock, flags);
> bitmap_release_region(mem->bitmap, page, order);
> + mem->avail += 1 << order;
> spin_unlock_irqrestore(&mem->spinlock, flags);
> return 1;
> }
>

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