[U-Boot] [PATCH v2 10/14] linux_compat: introduce GFP_DMA flag for kmalloc()

Masahiro Yamada
2015-07-13T08:03:56Z

2015-07-13 16:52 GMT+09:00 Lukasz Majewski <l.majewski@samsung.com>:
> Hi Masahiro,
>
>> It does not seem efficient to always return cache-aligned memory.
>> Return aligned memory only when GFP_DMA flag is given.
>>
>> My main motivation for this commit is to refactor device_probe()
>> and device_free() in the next commit. DM_FLAG_ALLOC_PRIV_DMA
>> should be handled more easily.
>>
>> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
>> ---
>>
>> Changes in v2: None
>>
>> include/linux/compat.h | 1 +
>> lib/linux_compat.c | 5 ++++-
>> 2 files changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/compat.h b/include/linux/compat.h
>> index fbebf91..13386c9 100644
>> --- a/include/linux/compat.h
>> +++ b/include/linux/compat.h
>> @@ -41,6 +41,7 @@ extern struct p_current *current;
>> #define GFP_NOFS ((gfp_t) 0)
>> #define GFP_USER ((gfp_t) 0)
>> #define __GFP_NOWARN ((gfp_t) 0)
>> +#define GFP_DMA ((__force gfp_t)0x01u)
>> #define __GFP_ZERO ((__force gfp_t)0x8000u) /* Return
>> zeroed page on success */
>> void *kmalloc(size_t size, int flags);
>> diff --git a/lib/linux_compat.c b/lib/linux_compat.c
>> index a936a7e..6da0cfa 100644
>> --- a/lib/linux_compat.c
>> +++ b/lib/linux_compat.c
>> @@ -18,7 +18,10 @@ void *kmalloc(size_t size, int flags)
>> {
>> void *p;
>>
>> - p = memalign(ARCH_DMA_MINALIGN, size);
>> + if (flags & GFP_DMA)
>> + p = memalign(ARCH_DMA_MINALIGN, size);
>> + else
>> + p = malloc(size);
>> if (flags & __GFP_ZERO)
>> memset(p, 0, size);
>>
>
> Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
>
> I hope that all places where kmalloc without GFP_DMA set is called
> and implicitly require memalign'ed memory would be changed accordingly.
>
> Otherwise we would have nasty, hard to find bugs.

As Lukasz and Heiko pointed out, I admit this commit is not safe.

For now, we should consider keeping the cache-alignment for all the cases.

--
Best Regards
Masahiro Yamada