Hi Marek,
On 10/17/2015 07:03 AM, Marek Vasut wrote:
I would suggest the "cache alignment check and skip" be removed from
cache flush ops, and say out the DMA buffer allocation rule loudly in
README, and enforce it by guardianship.
What exactly do you envision by this "guardianship" ?
I mean the reviews of custodians.
Please allow me to restate the reasons,
1. The cache flush ops are commonly used. Please refer to the "Cache and
TLB Flushing Under Linux" doc, linux/Documentation/cachetlb.txt.
Violating the defined interface is much worse than violating coding
style. It will certainly impact the portability of u-boot. And might
introduce more bug than resolve.
I agree with this one.
2. We all agree that enforcing DMA buffer allocation to cache aligned is
the only real solution. Adding such "check and skip" to cache flush ops
cannot prevent the flush or solve the problem.
We should probably check-scream-skip here.
3. Though the flush size of block device are usually aligned, the size
of packet are not. Asking the packet drivers to adjust the flush size
does not make sense. It is the job of cache flush ops. The debug probe
should not override the original purpose. It should be spelled for
common understanding.
The socket buffer(s) should be aligned, so network packets should be fine.
While the start of socket buffer might be aligned, the size of the
transfer might not for the send ops. It is depended on the net/tcp/ip
packets size.
For example, with tftp, there is a lot of unaligned end of packets.
tftp d1000000 u-boot-dtb.bin
flush unaligned d7ff7020-d7ff704e
[repeat ..]
So, such an alarm may be false. And such a skip can be bug.
In fact, for my own projects, I have changed the memory allocation to
always cache aligned. And I rarely worry about it ever after.
I look at the net.c of u-boot. There are packets buffer allocated on BSS
and stack. I would suggest avoid such programming, and use aligned
memory allocation stead.
Best regards,
Thomas
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