Re: [PATCH 1/1] dma-contiguous: return early for dt case in dma_contiguous_reserve

From: Robin Murphy
Date: Tue Jun 01 2021 - 14:48:51 EST


On 2021-05-31 10:21, Dong Aisheng wrote:
On Tue, May 18, 2021 at 7:29 PM Dong Aisheng <aisheng.dong@xxxxxxx> wrote:

dma_contiguous_reserve() aims to support cmdline case for CMA memory
reserve. But if users define reserved memory in DT,
'dma_contiguous_default_area' will not be 0, then it's meaningless
to continue to run dma_contiguous_reserve(). So we return early
if detect 'dma_contiguous_default_area' is unzero.

Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Cc: Robin Murphy <robin.murphy@xxxxxxx>
Signed-off-by: Dong Aisheng <aisheng.dong@xxxxxxx>

Gently ping

The commit message is still wrong, and I still think the change doesn't achieve anything meaningful. This code is hard to make sense of either way because the crucial interplay between size_cmdline and dma_contiguous_default_area is hidden somewhere else entirely, and it would take a much more significant refactoring to clear that up.

Robin.


Regards
Aisheng

---
kernel/dma/contiguous.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index 3d63d91cba5c..ebade9f43eff 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -171,6 +171,9 @@ void __init dma_contiguous_reserve(phys_addr_t limit)
phys_addr_t selected_limit = limit;
bool fixed = false;

+ if (dma_contiguous_default_area)
+ return;
+
pr_debug("%s(limit %08lx)\n", __func__, (unsigned long)limit);

if (size_cmdline != -1) {
@@ -191,7 +194,7 @@ void __init dma_contiguous_reserve(phys_addr_t limit)
#endif
}

- if (selected_size && !dma_contiguous_default_area) {
+ if (selected_size) {
pr_debug("%s: reserving %ld MiB for global area\n", __func__,
(unsigned long)selected_size / SZ_1M);

--
2.25.1