linux-kernel - [PATCH 2/2] dma-mapping: set default segment_boundary_mask to ULONG

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Date:   Tue,  1 Sep 2020 15:16:46 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     hch@....de
Cc:     sfr@...b.auug.org.au, mpe@...erman.id.au, benh@...nel.crashing.org,
        paulus@...ba.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, rth@...ddle.net,
        ink@...assic.park.msu.ru, mattst88@...il.com,
        linux-alpha@...r.kernel.org, tony.luck@...el.com,
        fenghua.yu@...el.com, linux-ia64@...r.kernel.org,
        schnelle@...ux.ibm.com, gerald.schaefer@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com, borntraeger@...ibm.com,
        linux-s390@...r.kernel.org, davem@...emloft.net,
        sparclinux@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com,
        James.Bottomley@...senPartnership.com, deller@....de,
        linux-parisc@...r.kernel.org
Subject: [PATCH 2/2] dma-mapping: set default segment_boundary_mask to ULONG_MAX

The default segment_boundary_mask was set to DMA_BIT_MAKS(32)
a decade ago by referencing SCSI/block subsystem, as a 32-bit
mask was good enough for most of the devices.

Now more and more drivers set dma_masks above DMA_BIT_MAKS(32)
while only a handful of them call dma_set_seg_boundary(). This
means that most drivers have a 4GB segmention boundary because
DMA API returns a 32-bit default value, though they might not
really have such a limit.

The default segment_boundary_mask should mean "no limit" since
the device doesn't explicitly set the mask. But a 32-bit mask
certainly limits those devices capable of 32+ bits addressing.

So this patch sets default segment_boundary_mask to ULONG_MAX.

Signed-off-by: Nicolin Chen <nicoleotsuka@...il.com>
---
 include/linux/dma-mapping.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index faab0a8210b9..df0bff2ea750 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -629,7 +629,7 @@ static inline unsigned long dma_get_seg_boundary(struct device *dev)
 {
 	if (dev->dma_parms && dev->dma_parms->segment_boundary_mask)
 		return dev->dma_parms->segment_boundary_mask;
-	return DMA_BIT_MASK(32);
+	return ULONG_MAX;
 }

 /**
-- 
2.17.1