On 31.07.2015 09:40, Lucas Stach wrote:
Hi Dirk,
Am Freitag, den 31.07.2015, 08:40 +0200 schrieb Dirk Behme:
On 19.05.2015 14:16, Fabio Estevam wrote:
Hi Philipp,
On Tue, May 19, 2015 at 5:54 AM, Philipp Zabel <p.zabel@xxxxxxxxxxxxxx> wrote:
The driver configures the IDLE condition to interrupt the SDMA engine.
Since the SDMA UART ROM script doesn't clear the IDLE bit itself, this
caused repeated 1-byte DMA transfers, regardless of available data in the
RX FIFO. Also, when returning due to the IDLE condition, the UART ROM
script already increased its counter, causing residue to be off by one.
This patch clears the IDLE condition to avoid repeated 1-byte DMA transfers
and decreases count by when the DMA transfer was aborted due to the IDLE
condition, fixing serial transfers using DMA on i.MX6Q.
Reported-by: Peter Seiderer <ps.report@xxxxxxx>
Signed-off-by: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>
Thanks for the fix. Tested on a imx6sl-warp, where I could not use DMA
to access a Bluetooth device using the ROM SDMA firmware.
Tested-by: Fabio Estevam <fabio.estevam@xxxxxxxxxxxxx>
Could you please also Cc stable?
Just fyi: We got this patch via -stable, and found that it results in
issues for us. So we had to revert it in our local tree.
We are using the DMA with baud rates > 2Mbit/s. Having a quick look at
the registers in the ARM Reference Manual, USR2_IDLE seems to be a flag
that is set when the RX line has been idle for at least a defined amount
of time.
For us this commit is dangerous because it fails to check whether the
IDLE CONDITION feature is being used. We don't use the RX IDLE CONDITION
feature, therefore it is likely to cause the last received character to
be discarded causing corruption of data.
From your description it's not clear to me why this commit is causing
issues for you. The idle condition signaling is automatically enabled
when using DMA.
The idle signaling should only ever fire if the line has been idle for
32byte durations. The aging timer, that expires after data is sitting in
the FIFO for 8 byte durations, should have flushed out all data at this
point.
Do you use a RAM SDMA firmware or do you rely on the internal one.
To my understanding we are using a RAM SDMA firmware. If I read the
various mailing list thread correctly, the difference between the RAM
SDMA firmware and the internal one was already often a root cause for
different behavior.
Best regards
Dirk
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