Re: [RFC PATCH v3 1/6] swiotlb: Add io_tlb_mem struct
From: Christoph Hellwig <hch@lst.de>
Date: 2021-01-13 11:51:33
Also in:
linux-devicetree, linux-iommu, lkml, xen-devel
On Wed, Jan 06, 2021 at 11:41:19AM +0800, Claire Chang wrote:
Added a new struct, io_tlb_mem, as the IO TLB memory pool descriptor and moved relevant global variables into that struct. This will be useful later to allow for restricted DMA pool.
I like where this is going, but a few comments. Mostly I'd love to be able to entirely hide io_tlb_default_mem and struct io_tlb_mem inside of swiotlb.c.
quoted hunk ↗ jump to hunk
--- a/arch/powerpc/platforms/pseries/svm.c +++ b/arch/powerpc/platforms/pseries/svm.c@@ -55,8 +55,8 @@ void __init svm_swiotlb_init(void) if (vstart && !swiotlb_init_with_tbl(vstart, io_tlb_nslabs, false)) return; - if (io_tlb_start) - memblock_free_early(io_tlb_start, + if (io_tlb_default_mem.start) + memblock_free_early(io_tlb_default_mem.start, PAGE_ALIGN(io_tlb_nslabs << IO_TLB_SHIFT));
I think this should switch to use the local vstart variable in prep patch.
quoted hunk ↗ jump to hunk
panic("SVM: Cannot allocate SWIOTLB buffer"); }diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c index 2b385c1b4a99..4d17dff7ffd2 100644 --- a/drivers/xen/swiotlb-xen.c +++ b/drivers/xen/swiotlb-xen.c@@ -192,8 +192,8 @@ int __ref xen_swiotlb_init(int verbose, bool early) /* * IO TLB memory already allocated. Just use it. */ - if (io_tlb_start != 0) { - xen_io_tlb_start = phys_to_virt(io_tlb_start); + if (io_tlb_default_mem.start != 0) { + xen_io_tlb_start = phys_to_virt(io_tlb_default_mem.start); goto end;
xen_io_tlb_start is interesting. It is used only in two functions:
1) is_xen_swiotlb_buffer, where I think we should be able to just use
is_swiotlb_buffer instead of open coding it with the extra
phys_to_virt/virt_to_phys cycle.
2) xen_swiotlb_init, where except for the assignment it only is used
locally for the case not touched above and could this be replaced
with a local variable.
Konrad, does this make sense to you?
static inline bool is_swiotlb_buffer(phys_addr_t paddr)
{
- return paddr >= io_tlb_start && paddr < io_tlb_end;
+ struct io_tlb_mem *mem = &io_tlb_default_mem;
+
+ return paddr >= mem->start && paddr < mem->end;We'd then have to move this out of line as well.