On Tue, Jan 26, 2010 at 6:44 PM, David Daney <ddaney@xxxxxxxxxxxxxxxxxx> wrote:
> Manuel Lauss wrote:
>>
>> DBDMA descriptors need to be located at 32-byte aligned addresses;
>> however kmalloc rarely delivers such addresses. The dbdma code
>> works around that by allocating 63 bytes and re-aligning the
>> descriptor base afterwards. Hoewever when freeing memory it does
>> not account for this adjustment and trips the kfree debugcheck:
>>
>
> Correct me if I am wrong, but don't kmalloc et al. return blocks aligned
> boundaries of the size rounded up the the next power of two? So if you
> need 32-byte aligned addresses, just use a size value of 32 or greater. You
> wouldn't have to add 63 and do masking and remember the membase value as you
> do in the patch.
The description is not completely correct (I suck a writing those):
It allocates a number
of descriptor entries (64 bytes each) specified by the driver in a single block:
desc_base = (u32)kmalloc(entries * sizeof(au1x_ddma_desc_t),
GFP_KERNEL|GFP_DMA);
if (desc_base == 0)
return 0;
if (desc_base & 0x1f) {
So far the 3 users I have (mmc, spi, audio) always return true on the above
check (2 descriptors for audio for instance).
Manuel
