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

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Message-ID: <CAHp75VcoJh51ai_35vB_V7exyFwRT0NjKcs=a0TAdaU8+FuzwA@mail.gmail.com>
Date:	Fri, 13 Nov 2015 03:26:01 +0200
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	"Matwey V. Kornilov" <matwey@....msu.ru>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	jslaby@...e.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>
Subject: Re: [PATCH v3 2/5] tty: Introduce SER_RS485_SOFTWARE read-only flag
 for struct serial_rs485

On Fri, Nov 13, 2015 at 3:11 AM, Peter Hurley <peter@...leysoftware.com> wrote:
> On 11/12/2015 07:41 PM, Andy Shevchenko wrote:
>> On Thu, Nov 12, 2015 at 10:22 PM, Peter Hurley <peter@...leysoftware.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
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