Re: [RFC PATCH v3 2/6] swiotlb: Add restricted DMA pool

On Wed, Jan 13, 2021 at 8:42 PM Christoph Hellwig [off-list ref] wrote:

quoted

+#ifdef CONFIG_SWIOTLB
+     struct io_tlb_mem       *dma_io_tlb_mem;
 #endif

Please add a new config option for this code instead of always building
it when swiotlb is enabled.

quoted

+static int swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, phys_addr_t start,
+                                size_t size)

Can you split the refactoring in swiotlb.c into one or more prep
patches?

quoted

+static int rmem_swiotlb_device_init(struct reserved_mem *rmem,
+                                 struct device *dev)
+{
+     struct io_tlb_mem *mem = rmem->priv;
+     int ret;
+
+     if (dev->dma_io_tlb_mem)
+             return -EBUSY;
+
+     if (!mem) {
+             mem = kzalloc(sizeof(*mem), GFP_KERNEL);
+             if (!mem)
+                     return -ENOMEM;

What is the calling convention here that allows for a NULL and non-NULL
private data?

Since multiple devices can share the same pool, the private data,
io_tlb_mem struct, will be initialized by the first device attached to
it.
This is similar to rmem_dma_device_init() in kernel/dma/coherent.c.
I'll add a comment for it in next version.