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

From: Marek Szyprowski
Date: Wed Jul 30 2014 - 01:33:45 EST

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.

If it is a risk, then the alternative would be to put an explicit
dma_coherent_mem pointer into the reserved_mem structure.

If one messes with priv pointers, he should expect serious problems and we really
cannot prevent him anyway.

+ if (!mem &&
+ dma_init_coherent_memory(rmem->base, rmem->base, rmem->size,
+ DMA_MEMORY_MAP | DMA_MEMORY_EXCLUSIVE,
+ &mem) != DMA_MEMORY_MAP) {
+ pr_info("Reserved memory: failed to init DMA memory pool at %pa, size %ld MiB\n",
+ &rmem->base, (unsigned long)rmem->size / SZ_1M);
+ return;
+ }
+ rmem->priv = mem;
+ dma_assign_coherent_memory(dev, mem);
+}
+
+static void rmem_dma_device_release(struct reserved_mem *rmem,
+ struct device *dev)
+{
+ dev->dma_mem = NULL;
+}
+
+static const struct reserved_mem_ops rmem_dma_ops = {
+ .device_init = rmem_dma_device_init,
+ .device_release = rmem_dma_device_release,
+};
+
+static int __init rmem_dma_setup(struct reserved_mem *rmem)
+{
+ unsigned long node = rmem->fdt_node;
+
+ if (of_get_flat_dt_prop(node, "reusable", NULL))
+ return -EINVAL;
+
+ rmem->ops = &rmem_dma_ops;
+ pr_info("Reserved memory: created DMA memory pool at %pa, size %ld MiB\n",
+ &rmem->base, (unsigned long)rmem->size / SZ_1M);
+ return 0;
+}
+RESERVEDMEM_OF_DECLARE(dma, "shared-dma-pool", rmem_dma_setup);
+#endif
--
1.9.2

Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland

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