linux-kernel - Re: [PATCH?][arch/parisc/kernel/pci-dma.c] pcxl_dma_ops.alloc

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Date:	Mon, 11 Feb 2008 19:56:10 +0100
From:	Roel Kluin <12o3l@...cali.nl>
To:	John David Anglin <dave@...uly1.hia.nrc.ca>
CC:	James.Bottomley@...senPartnership.com, kyle@...isc-linux.org,
	matthew@....cx, grundler@...isc-linux.org,
	linux-parisc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH?][arch/parisc/kernel/pci-dma.c]      pcxl_dma_ops.alloc_noncoherent

John David Anglin wrote:
>> James Bottomley wrote:
>>> On Mon, 2008-02-11 at 17:23 +0100, Roel Kluin wrote:
>>>> duplicate pa11_dma_alloc_consistent; more appropriate appears
>>>> pa11_dma_alloc_noncoherent here. 
>>>>
>>>> Not tested, please confirm that this fix is correct
>>> No, it looks completely incorrect to me.  What makes you think a pcxl
>>> box has a problem with coherency?
>> Ok, please ignore the patch then. It just appeared suspicious to me
>> that the function did exist, but the names assigned were different.
> 
> How about a comment?

Based on James Bottomley's explanation maybe a comment like this?
---
Explain why dma_alloc_noncoherent is only used for boxes PA7200 and below

Signed-off-by: Roel Kluin <12o3l@...cali.nl>
---
diff --git a/arch/parisc/kernel/pci-dma.c b/arch/parisc/kernel/pci-dma.c
index 9448d4e..fc3325a 100644
--- a/arch/parisc/kernel/pci-dma.c
+++ b/arch/parisc/kernel/pci-dma.c
@@ -567,6 +567,10 @@ static void *fail_alloc_consistent(struct device *dev, size_t size,
 	return NULL;
 }
 
+/*
+ * dma_alloc_noncoherent is a fallback for boxes PA7200 and below which
+ * cannot allocate coherent memory.
+ */
 static void *pa11_dma_alloc_noncoherent(struct device *dev, size_t size,
 					  dma_addr_t *dma_handle, gfp_t flag)
 {
@@ -586,6 +590,10 @@ static void pa11_dma_free_noncoherent(struct device *dev, size_t size,
 	return;
 }
 
+/*
+ * PCXL allocates coherent memory even for dma_alloc_noncoherent() due to the
+ * uncached trick for coherent memory.
+ */
 struct hppa_dma_ops pcx_dma_ops = {
 	.dma_supported =	pa11_dma_supported,
 	.alloc_consistent =	fail_alloc_consistent,

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