linux-kernel - Re: [PATCH] drm: radeon: r600_dma: Replace cpu_to_le32() by lower_32

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Date:   Mon, 16 Aug 2021 14:47:18 +0200
From:   Christian König <ckoenig.leichtzumerken@...il.com>
To:     Michel Dänzer <michel@...nzer.net>,
        zhaoxiao <zhaoxiao@...ontech.com>, airlied@...ux.ie
Cc:     alexander.deucher@....com, christian.koenig@....com,
        David1.Zhou@....com, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: radeon: r600_dma: Replace cpu_to_le32() by
 lower_32_bits()



Am 13.08.21 um 17:03 schrieb Michel Dänzer:
> On 2021-08-13 10:54 a.m., zhaoxiao wrote:
>> This patch fixes the following sparse errors:
>> drivers/gpu/drm/radeon/r600_dma.c:247:30: warning: incorrect type in assignment (different base types)
>> drivers/gpu/drm/radeon/r600_dma.c:247:30:    expected unsigned int volatile [usertype]
>> drivers/gpu/drm/radeon/r600_dma.c:247:30:    got restricted __le32 [usertype]
>>
>> Signed-off-by: zhaoxiao <zhaoxiao@...ontech.com>
>> ---
>>   drivers/gpu/drm/radeon/r600_dma.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/radeon/r600_dma.c b/drivers/gpu/drm/radeon/r600_dma.c
>> index fb65e6fb5c4f..a2d0b1edcd22 100644
>> --- a/drivers/gpu/drm/radeon/r600_dma.c
>> +++ b/drivers/gpu/drm/radeon/r600_dma.c
>> @@ -244,7 +244,7 @@ int r600_dma_ring_test(struct radeon_device *rdev,
>>   	gpu_addr = rdev->wb.gpu_addr + index;
>>   
>>   	tmp = 0xCAFEDEAD;
>> -	rdev->wb.wb[index/4] = cpu_to_le32(tmp);
>> +	rdev->wb.wb[index/4] = lower_32_bits(tmp);
>>   
>>   	r = radeon_ring_lock(rdev, ring, 4);
>>   	if (r) {
>>
> Seems better to mark rdev->wb.wb as little endian instead. It's read with le32_to_cpu (with some exceptions which look like bugs), which would result in 0xADEDFECA like this.

Yeah, that patch doesn't look correct at all and most likely breaks ring 
test on big endian systems.

Christian.