Re: Mainline commit "serial: Test for no tx data on tx restart" not correct for i.MX6?

[jiwang <jiada_wang@mentor.com>]

Hi Peter

On 07/24/2014 01:32 AM, Peter Hurley wrote:
> Hi Dirk,
>
> On 07/23/2014 12:10 AM, Dirk Behme wrote:
>> Hi,
>>
>> this is a question regarding the i.MX6 part (drivers/tty/serial/imx.c) of the commit
>>
>> serial: Test for no tx data on tx restart
>>
>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c557d392fbf5badd693ea1946a4317c87a26a716
>>
>> Talking with some i.MX6 experts about this, I've got the comment
>>
>> -- cut --
>> The imx serial driver part of this commit isn't correct
>> as imx.c sends x_char in irq handler, not in imx_start_tx(),
>> -- cut --
>>
>> What do you think?
> Thanks for the comment.
>
> Yeah, I missed that the imx driver handled x_char _at all_,
> because how the imx driver is handling x_char looks broken.
>
> For example, if data is already in the tx ring buffer,
> imx_start_tx() will send that data before the x_char, and if
> all the tx ring buffer data is sent successfully, the tx
> interrupt is switched back off, so the x_char won't be sent.
imx_start_tx() doesn't do any actual data transfer, it only
switches tx interrupt on, and tx interrupt does the actual data
transfer, so if x_char is pending, it will always be sent before
the data in ring buffer.
> Also, the imx driver doesn't send x_char in dma mode?
Yes, I think so.

Thanks,
Jiada
> Regards,
> Peter Hurley
>