RE: [PATCH V3 1/2] i2c: qup: Fix broken dma when CONFIG_DEBUG_SG is enabled

From: Sricharan
Date: Thu May 26 2016 - 18:01:26 EST


>> sg_set_buf expects that the buf parameter passed in should be from
>> lowmem and a valid pageframe. This is not true for pages from
>> dma_alloc_coherent which can be carveouts, hence the check fails.
>OK, given you mean dma_pool_alloc here, the check fails for the
>pageframe because of the pool? Is my understanding correct?
Yes right. Since those are carveouts, there is no valid pageframe,
so the check fails.

>> Change allocation of sg buffers from dma_coherent memory to kzalloc
>> to fix the issue.
>But why can you drop the coherency?
The coherency is not dropped here. dma_map/unmap used
makes the buffer coherent before passing it to
dmaengine. Previously it was not required.
I can add this in description if its not clear.

>> @@ -1268,6 +1260,8 @@ static int qup_i2c_xfer_v2(struct i2c_adapter *adap,
>> }
>> }
>> + idx = 0;
>> +
>This looks like an unrelated change.
Ha, wrong. This should have been in a separate patch. This was to fix a
initialization issue in dma mode. Sorry, should not have been here, will
move it to out.