Here's my current code:
https://github.com/cyndis/linux/commits/wip/t194-tcu-4
"fixup! mailbox: tegra-hsp: Add support for shared mailboxes" splits up
the controller into two. "tegra-hsp: use polling" changes it to use polling.
There are two lines in the top patch with comments:
- at the end of tegra_hsp_mailbox_send_data, I left a "while
(!tegra_hsp_mailbox_last_tx_done(chan));". Without it I wasn't able to
see even a few garbled characters in the output.
- as mentioned, if I enable tx_block on the client side, I get a BUG:
scheduling while atomic. I assume this gets printed through the earlycon
as it's printing out correctly.
Thanks,
Mikko
On 08.08.2018 17:46, Mikko Perttunen wrote:
On 08/08/2018 05:39 PM, Jassi Brar wrote:
On Wed, Aug 8, 2018 at 8:04 PM, Mikko Perttunen <cyndis@xxxxxxxx> wrote:
On 08/08/2018 05:10 PM, Jassi Brar wrote:
On Wed, Aug 8, 2018 at 5:08 PM, Mikko Perttunen <cyndis@xxxxxxxx>
wrote:
On 04.08.2018 13:45, Mikko Perttunen wrote:
On 08/03/2018 03:54 PM, Jassi Brar wrote:
On Mon, Jul 2, 2018 at 5:10 PM, Mikko Perttunen
<mperttunen@xxxxxxxxxx>
wrote:
Add a new TXDONE option, TXDONE_BY_BLOCK. With this option, the
send_data function of the mailbox driver is expected to block until
the message has been sent. The new option is used with the Tegra
Combined UART driver to minimize unnecessary overhead when
transmitting
data.
1) TXDONE_BY_BLOCK flag :-
Have you tried setting the flag
mbox_chan->mbox_client->tx_block
?
No - I suppose I should have done that. I'm a bit concerned about
overhead
as send_data may be called thousands of times per second, so I
tried to
make
it as close as possible to the downstream driver that just pokes the
mailbox
register directly.
I tried using polling in the mailbox framework. Some printing is done
from
atomic context so it seems tx_block cannot be used -
wait_for_completion_timeout understandably does not work in atomic
context.
I also tried without tx_block, in which case I got some horribly
garbled
output, but "Try increasing MBOX_TX_QUEUE_LEN" was readable there.
Any opinions?
The problems arise because your hardware (SM) supports TXDONE_BY_POLL,
but your client drives it by TXDONE_BY_ACK because the older DB
channels are so.
Please populate SM channels as a separate controller than DB.
The DB controller, as is, run by ACK method.
The SM controller should be run by polling, i.e, set txdone_poll =
true and the poll period small enough. The virtual tty client driver
should be able to safely set tx_block from appropriate context.
Sorry, I should have clarified that I already split up the
controllers. The
SM controller has txdone_poll = true. I didn't adjust txpoll_period so I
guess it's zero.
Can you please share your code (controller and client) ? Maybe offline
if you wish.
I'll upload a git branch tomorrow -- I'm not at the machine with the
code now.
Mikko
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