linux-kernel - Re: [PATCH 1/1] Add strong pullup emulation to w1-gpio master driver.

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Date:	Tue, 12 Nov 2013 05:07:14 +0400
From:	Evgeny Boger <eugenyboger@...il.com>
To:	Evgeniy Polyakov <zbr@...emap.net>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Fries <david@...es.net>
Subject: Re: [PATCH 1/1] Add strong pullup emulation to w1-gpio master driver.

+David Fries <david@...es.net>

Hi David,

Would you please comment on this?


11/12/2013 05:03 AM, Evgeniy Polyakov:
> Hi
>
> 12.11.2013, 03:32, "Evgeny Boger" <eugenyboger@...il.com>:
>>> Why did you drop this check? It has nothing with w1-gpio driver
>> This check prevents master from implementing "set_pullup"  provided it does support only "write_bit" method.
>> The comment above states that
>>>   w1_io.c would need to support calling set_pullup before - * the last write_bit operation of a w1_write_8 which it currently - * doesn't.
>> which is kind of strange, since it describes what w1_io.c actually does support.
>>
>> w1_write_8 (w1_io.c:154, https://github.com/torvalds/linux/blob/master/drivers/w1/w1_io.c#L154):
>>>                  for (i = 0; i < 8; ++i) {
>>>                          if (i == 7)
>>>                                  w1_pre_write(dev);
>>>                          w1_touch_bit(dev, (byte >> i) & 0x1);
>>>                  }
>> It seems like w1_write_8() calls w1_pre_write(), which in turn calls set_pullup() just before the last write_bit().
>>
>> I'm not sure why this check was there in the first place.
> Please add author of those lines to clarify things.
> This doesn't look obvious to me

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