linux-kernel - Re: CONFIG_DMA_NOOP

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Message-ID: <04535c78-d418-b2b2-89db-ab4732a05984@infradead.org>
Date:   Sun, 15 Oct 2017 20:58:24 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Marian Mihailescu <marian.mihailescu@...laide.edu.au>,
        linux-kernel@...r.kernel.org
Cc:     Bart Van Assche <bart.vanassche@...disk.com>,
        iommu@...ts.linux-foundation.org,
        Vladimir Murzin <vladimir.murzin@....com>
Subject: Re: CONFIG_DMA_NOOP_OPS breaks ARM arch

On 10/15/17 20:29, Randy Dunlap wrote:
> On 10/15/17 20:27, Randy Dunlap wrote:
>> On 10/15/17 19:27, Marian Mihailescu wrote:
>>> After commit 7844572c633964c864d9f32dc3f2a8ffe5d70371, dma_noop_ops
>>> are built only for architectures that use it.
>>>
>>> For ARM architecture, CONFIG_DMA_NOOP_OPS is not selected, and cannot
>>> be selected.

What kernel version are you looking at?
I see that it is selected:

--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -22,6 +22,7 @@ config ARM
 	select CLONE_BACKWARDS
 	select CPU_PM if (SUSPEND || CPU_IDLE)
 	select DCACHE_WORD_ACCESS if HAVE_EFFICIENT_UNALIGNED_ACCESS
+	select DMA_NOOP_OPS if !MMU
 	select EDAC_SUPPORT
 	select EDAC_ATOMIC_SCRUB
 	select GENERIC_ALLOCATOR


That's in commit ID 1c51c429f30ea10428337f3a33c12059ba59f668 from May 24, 2017.

>>> However, arch/arm/include/asm/dma-mapping.h is referencing dma_noop_ops:
>>>
>>> static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)
>>> {
>>> return IS_ENABLED(CONFIG_MMU) ? &arm_dma_ops : &dma_noop_ops;
>>> }
>>>
>>> I will let a maintainer suggest the best resolution for this :)
>>>
>>
>> add Bart and iommu mailing list.
>>
> 
> and add Vladimir.
> 
> 


-- 
~Randy