linux-kernel - [RFC 4/5] dma-direct: Allocate dma pages directly if global pool allocation fails

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Date:   Fri, 23 Jul 2021 14:40:30 -0700
From:   Atish Patra <atish.patra@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Atish Patra <atish.patra@....com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Christoph Hellwig <hch@....de>, devicetree@...r.kernel.org,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Frank Rowand <frowand.list@...il.com>,
        Guo Ren <guoren@...ux.alibaba.com>,
        iommu@...ts.linux-foundation.org, linux-riscv@...ts.infradead.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Rob Herring <robh+dt@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Tobias Klauser <tklauser@...tanz.ch>
Subject: [RFC 4/5] dma-direct: Allocate dma pages directly if global pool allocation fails

DMA_GLOBAL_POOL config may be enabled for platforms where global pool is
not supported because a generic defconfig is expected to boot on different
platforms. Specifically, some RISC-V platforms may use global pool for
non-coherent devices while some other platforms are completely coherent.
However, it is expected that single kernel image must boot on all the
platforms.

Continue the dma direct allocation if a allocation from global pool failed.
This indicates that the platform is relying on some other method (direct
remap) or just have coherent devices.

Signed-off-by: Atish Patra <atish.patra@....com>
---
 kernel/dma/direct.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index d1d0258ed6d0..984ea776f099 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -161,8 +161,11 @@ void *dma_direct_alloc(struct device *dev, size_t size,
 		return arch_dma_alloc(dev, size, dma_handle, gfp, attrs);
 
 	if (IS_ENABLED(CONFIG_DMA_GLOBAL_POOL) &&
-	    !dev_is_dma_coherent(dev))
-		return dma_alloc_from_global_coherent(dev, size, dma_handle);
+	    !dev_is_dma_coherent(dev)) {
+		ret = dma_alloc_from_global_coherent(dev, size, dma_handle);
+		if (ret)
+			return ret;
+	}
 
 	/*
 	 * Remapping or decrypting memory may block. If either is required and
-- 
2.31.1