Re: [PATCH v3 2/5] tty: Introduce SER_RS485_SOFTWARE read-only flag for struct serial_rs485

Andy Shevchenko
2015-11-13T01:26:05Z

On Fri, Nov 13, 2015 at 3:11 AM, Peter Hurley <peter@hurleysoftware.com> wrote:
> On 11/12/2015 07:41 PM, Andy Shevchenko wrote:
>> On Thu, Nov 12, 2015 at 10:22 PM, Peter Hurley <peter@hurleysoftware.com> wrote:
>>> On 11/12/2015 02:57 PM, One Thousand Gnomes wrote:
>>
>>> An illustrative (kernel-space) example is the mess that is dmaengine_pause().
>>> Some DMA implementations provide the means to stop and restart DMA without
>>> losing data and some DMA implementations do not. Unfortunately, some
>>> advertise they support dmaengine_pause() but only for lossy uses like audio.
>>> Because the api hides this, the query interface for pause support is
>>> useless.
>>
>> The DMA pause() call means only pause with possibility to resume.
>> There is a resume() call as well. Any driver which treats pause() as a
>> complete stop is buggy driver and should be fixed.
>
> How about pause _without_ the possibility to resume?
>
> https://groups.google.com/d/msg/linux.kernel/Abe0hfGcgsw/H0se55wC558J

Briefly what I got from the thread that Russel shows similar view on
the API, so that's why he was objecting to add pause/resume calls for
a specific hardware.

--
With Best Regards,
Andy Shevchenko