Re: [PATCH v2 RESEND 3/4] drivers: dma-coherent: add initialization from device tree

[Grant Likely]

On Tue, Jul 29, 2014 at 11:33 PM, Marek Szyprowski
<m.szyprowski@xxxxxxxxxxx> wrote:
> Hello,
>
>
> On 2014-07-29 23:54, Grant Likely wrote:
>>
>> On Mon, 14 Jul 2014 10:28:06 +0200, Marek Szyprowski
>> <m.szyprowski@xxxxxxxxxxx> wrote:
>>>
>>> Initialization procedure of dma coherent pool has been split into two
>>> parts, so memory pool can now be initialized without assigning to
>>> particular struct device. Then initialized region can be assigned to
>>> more than one struct device. To protect from concurent allocations from
>>> different devices, a spinlock has been added to dma_coherent_mem
>>> structure. The last part of this patch adds support for handling
>>> 'shared-dma-pool' reserved-memory device tree nodes.
>>>
>>> Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
>>
>> I think this looks okay. It isn't in my area of expertise though.
>> Comments below.
>>
>>> ---
>>>   drivers/base/dma-coherent.c | 137
>>> ++++++++++++++++++++++++++++++++++++++------
>>>   1 file changed, 118 insertions(+), 19 deletions(-)
>>>
>>> diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c
>>> index 7d6e84a51424..7185a4f247e1 100644
>>> --- a/drivers/base/dma-coherent.c
>>> +++ b/drivers/base/dma-coherent.c
>>> @@ -14,11 +14,14 @@ struct dma_coherent_mem {
>>>         int             size;
>>>         int             flags;
>>>         unsigned long   *bitmap;
>>> +       spinlock_t      spinlock;
>>>   };
>>>   -int dma_declare_coherent_memory(struct device *dev, phys_addr_t
>>> phys_addr,
>>> -                               dma_addr_t device_addr, size_t size, int
>>> flags)
>>> +static int dma_init_coherent_memory(phys_addr_t phys_addr, dma_addr_t
>>> device_addr,
>>> +                            size_t size, int flags,
>>> +                            struct dma_coherent_mem **mem)
>>
>> This is a bit odd. Why wouldn't you return the dma_mem pointer directly
>> instead of passing in a **mem argument?
>
>
> Because this function (as a direct successor of dma_declare_coherent_memory)
> doesn't
> return typical error codes, but some custom values like DMA_MEMORY_MAP,
> DMA_MEMORY_IO
> or zero (which means failure). I wanted to avoid confusion with typical
> error
> handling path and IS_ERR/ERR_PTR usage used widely in other functions. This
> probably
> should be unified with the rest of kernel some day, but right now I wanted
> to keep
> the patch simple and easy to review.
>
>
>>>   {
>>> +       struct dma_coherent_mem *dma_mem = NULL;
>>>         void __iomem *mem_base = NULL;
>>>         int pages = size >> PAGE_SHIFT;
>>>         int bitmap_size = BITS_TO_LONGS(pages) * sizeof(long);
>>> @@ -27,27 +30,26 @@ int dma_declare_coherent_memory(struct device *dev,
>>> phys_addr_t phys_addr,
>>>                 goto out;
>>>         if (!size)
>>>                 goto out;
>>> -       if (dev->dma_mem)
>>> -               goto out;
>>> -
>>> -       /* FIXME: this routine just ignores DMA_MEMORY_INCLUDES_CHILDREN
>>> */
>>>         mem_base = ioremap(phys_addr, size);
>>>         if (!mem_base)
>>>                 goto out;
>>>   -     dev->dma_mem = kzalloc(sizeof(struct dma_coherent_mem),
>>> GFP_KERNEL);
>>> -       if (!dev->dma_mem)
>>> +       dma_mem = kzalloc(sizeof(struct dma_coherent_mem), GFP_KERNEL);
>>> +       if (!dma_mem)
>>>                 goto out;
>>> -       dev->dma_mem->bitmap = kzalloc(bitmap_size, GFP_KERNEL);
>>> -       if (!dev->dma_mem->bitmap)
>>> +       dma_mem->bitmap = kzalloc(bitmap_size, GFP_KERNEL);
>>> +       if (!dma_mem->bitmap)
>>>                 goto free1_out;
>>>   -     dev->dma_mem->virt_base = mem_base;
>>> -       dev->dma_mem->device_base = device_addr;
>>> -       dev->dma_mem->pfn_base = PFN_DOWN(phys_addr);
>>> -       dev->dma_mem->size = pages;
>>> -       dev->dma_mem->flags = flags;
>>> +       dma_mem->virt_base = mem_base;
>>> +       dma_mem->device_base = device_addr;
>>> +       dma_mem->pfn_base = PFN_DOWN(phys_addr);
>>> +       dma_mem->size = pages;
>>> +       dma_mem->flags = flags;
>>> +       spin_lock_init(&dma_mem->spinlock);
>>> +
>>> +       *mem = dma_mem;
>>>         if (flags & DMA_MEMORY_MAP)
>>>                 return DMA_MEMORY_MAP;
>>> @@ -55,12 +57,51 @@ int dma_declare_coherent_memory(struct device *dev,
>>> phys_addr_t phys_addr,
>>>         return DMA_MEMORY_IO;
>>>      free1_out:
>>> -       kfree(dev->dma_mem);
>>> +       kfree(dma_mem);
>>>    out:
>>>         if (mem_base)
>>>                 iounmap(mem_base);
>>>         return 0;
>>>   }
>>> +
>>> +static void dma_release_coherent_memory(struct dma_coherent_mem *mem)
>>> +{
>>> +       if (!mem)
>>> +               return;
>>> +       iounmap(mem->virt_base);
>>> +       kfree(mem->bitmap);
>>> +       kfree(mem);
>>> +}
>>> +
>>> +static int dma_assign_coherent_memory(struct device *dev,
>>> +                                     struct dma_coherent_mem *mem)
>>> +{
>>> +       if (dev->dma_mem)
>>> +               return -EBUSY;
>>> +
>>> +       dev->dma_mem = mem;
>>> +       /* FIXME: this routine just ignores DMA_MEMORY_INCLUDES_CHILDREN
>>> */
>>> +
>>> +       return 0;
>>> +}
>>> +
>>> +int dma_declare_coherent_memory(struct device *dev, phys_addr_t
>>> phys_addr,
>>> +                               dma_addr_t device_addr, size_t size, int
>>> flags)
>>> +{
>>> +       struct dma_coherent_mem *mem;
>>> +       int ret;
>>> +
>>> +       ret = dma_init_coherent_memory(phys_addr, device_addr, size,
>>> flags,
>>> +                                      &mem);
>>> +       if (ret == 0)
>>> +               return 0;
>>> +
>>> +       if (dma_assign_coherent_memory(dev, mem) == 0)
>>> +               return ret;
>>> +
>>> +       dma_release_coherent_memory(mem);
>>> +       return 0;
>>> +}
>>>   EXPORT_SYMBOL(dma_declare_coherent_memory);
>>>     void dma_release_declared_memory(struct device *dev)
>>> @@ -69,10 +110,8 @@ void dma_release_declared_memory(struct device *dev)
>>>         if (!mem)
>>>                 return;
>>> +       dma_release_coherent_memory(mem);
>>>         dev->dma_mem = NULL;
>>> -       iounmap(mem->virt_base);
>>> -       kfree(mem->bitmap);
>>> -       kfree(mem);
>>>   }
>>>   EXPORT_SYMBOL(dma_release_declared_memory);
>>>   @@ -80,6 +119,7 @@ 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;
>>> +       unsigned long flags;
>>>         int pos, err;
>>>         size += device_addr & ~PAGE_MASK;
>>> @@ -87,8 +127,11 @@ void *dma_mark_declared_memory_occupied(struct device
>>> *dev,
>>>         if (!mem)
>>>                 return ERR_PTR(-EINVAL);
>>>   +     spin_lock_irqsave(&mem->spinlock, flags);
>>>         pos = (device_addr - mem->device_base) >> PAGE_SHIFT;
>>>         err = bitmap_allocate_region(mem->bitmap, pos, get_order(size));
>>> +       spin_unlock_irqrestore(&mem->spinlock, flags);
>>> +
>>>         if (err != 0)
>>>                 return ERR_PTR(err);
>>>         return mem->virt_base + (pos << PAGE_SHIFT);
>>> @@ -115,6 +158,7 @@ int dma_alloc_from_coherent(struct device *dev,
>>> ssize_t size,
>>>   {
>>>         struct dma_coherent_mem *mem;
>>>         int order = get_order(size);
>>> +       unsigned long flags;
>>>         int pageno;
>>>         if (!dev)
>>> @@ -124,6 +168,7 @@ int dma_alloc_from_coherent(struct device *dev,
>>> ssize_t size,
>>>                 return 0;
>>>         *ret = NULL;
>>> +       spin_lock_irqsave(&mem->spinlock, flags);
>>>         if (unlikely(size > (mem->size << PAGE_SHIFT)))
>>>                 goto err;
>>> @@ -138,10 +183,12 @@ int dma_alloc_from_coherent(struct device *dev,
>>> ssize_t size,
>>>         *dma_handle = mem->device_base + (pageno << PAGE_SHIFT);
>>>         *ret = mem->virt_base + (pageno << PAGE_SHIFT);
>>>         memset(*ret, 0, size);
>>> +       spin_unlock_irqrestore(&mem->spinlock, flags);
>>>         return 1;
>>>     err:
>>> +       spin_unlock_irqrestore(&mem->spinlock, flags);
>>>         /*
>>>          * In the case where the allocation can not be satisfied from the
>>>          * per-device area, try to fall back to generic memory if the
>>> @@ -171,8 +218,11 @@ int dma_release_from_coherent(struct device *dev,
>>> int order, void *vaddr)
>>>         if (mem && vaddr >= mem->virt_base && vaddr <
>>>                    (mem->virt_base + (mem->size << PAGE_SHIFT))) {
>>>                 int page = (vaddr - mem->virt_base) >> PAGE_SHIFT;
>>> +               unsigned long flags;
>>>   +             spin_lock_irqsave(&mem->spinlock, flags);
>>>                 bitmap_release_region(mem->bitmap, page, order);
>>> +               spin_unlock_irqrestore(&mem->spinlock, flags);
>>>                 return 1;
>>>         }
>>>         return 0;
>>> @@ -218,3 +268,52 @@ int dma_mmap_from_coherent(struct device *dev,
>>> struct vm_area_struct *vma,
>>>         return 0;
>>>   }
>>>   EXPORT_SYMBOL(dma_mmap_from_coherent);
>>> +
>>> +/*
>>> + * Support for reserved memory regions defined in device tree
>>> + */
>>> +#ifdef CONFIG_OF_RESERVED_MEM
>>> +#include <linux/of.h>
>>> +#include <linux/of_fdt.h>
>>> +#include <linux/of_reserved_mem.h>
>>> +
>>> +static void rmem_dma_device_init(struct reserved_mem *rmem, struct
>>> device *dev)
>>> +{
>>> +       struct dma_coherent_mem *mem = rmem->priv;
>>
>> Will the reserved_mem->priv pointer ever point to some other kind of
>> structure? How do we know that the pointer here is always a
>> dma_coherent_mem struct (if there are other uses of priv, what is the
>> guarantee against another user assigning something to it?) Is it the
>> reserved_mem_ops below that provide the guarantee?
>
>
> reserved_mem_ops are set by the given reserved memory driver and access to
> priv
> pointer is limited only to that driver. This pattern is used widely across
> the
> whole kernel, so I don't think that a separate pointer to particular
> structure
> type is needed.

Yup, that's fine. I wanted to make sure.

Do I need to be taking these patches through the DT tree? Do patches 3
& 4 make sense without patch 2?

g.
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