Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1320296 > unrolled thread

RE: [PATCH V7 3/6] i2c: qup: Transfer each i2c_msg in i2c_msgs without a stop bit

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  RE: [PATCH V7 3/6] i2c: qup: Transfer each i2c_msg in i2c_msgs without a stop bit "Sricharan" <sricharan@codeaurora.org> - 2016-01-28 06:00 +0100
    Re: [PATCH V7 3/6] i2c: qup: Transfer each i2c_msg in i2c_msgs  without a stop bit Wolfram Sang <wsa@the-dreams.de> - 2016-02-04 21:10 +0100
      RE: [PATCH V7 3/6] i2c: qup: Transfer each i2c_msg in i2c_msgs without a stop bit "Sricharan" <sricharan@codeaurora.org> - 2016-02-05 09:10 +0100

#1320296 — RE: [PATCH V7 3/6] i2c: qup: Transfer each i2c_msg in i2c_msgs without a stop bit

Hi Wolfram,

> -----Original Message-----
> From: Wolfram Sang [mailto:wsa@the-dreams.de]
> Sent: Sunday, January 24, 2016 4:59 PM
> To: Sricharan R
> Cc: devicetree@vger.kernel.org; linux-arm-msm@vger.kernel.org;
> agross@codeaurora.org; linux-kernel@vger.kernel.org; linux-
> i2c@vger.kernel.org; iivanov@mm-sol.com; galak@codeaurora.org;
> dmaengine@vger.kernel.org; linux-arm-kernel@lists.infradead.org;
> andy.gross@linaro.org; ntelkar@codeaurora.org; architt@codeaurora.org
> Subject: Re: [PATCH V7 3/6] i2c: qup: Transfer each i2c_msg in i2c_msgs
> without a stop bit
> 
> Hi,
> 
> > "If this is the last message in a group, it is followed by a STOP.
> > Otherwise it is followed by the next @i2c_msg transaction segment,
> > beginning with a (repeated) START"
> 
> This is correct.
> 
> > So the expectation is that there is no 'STOP' bit inbetween individual
> > i2c_msg segments with repeated 'START'. The QUP i2c hardware has no
> > way to inform that there should not be a 'STOP' at the end of
transaction.
> > The only way to implement this is to coalesce all the i2c_msg in
> > i2c_msgs in to one transaction and transfer them. Adding the support for
> the same.
> 
> So, there will not be a REP_START condition on the bus? I am sorry to say
that
> I can't accept this. A REP_START is a REP_START and nothing else. There
are
> devices which will get confused if there is no real REP_START condition.
> 
> Without knowing the HW in detail, can't you implement I2C_M_NOSTART
> and let the touchscreen driver use it via regmap? That would be the proper
> way (from what I understand).


Ah, so what I meant above is there is no 'STOP' bit between each msg in
i2c_msgs, 
but 'REAPEATED_START' still holds true.  We are sending 'START' bit for each
msg.
So these is how each msg in i2c_msg is sent,

|------MSG1--------|-----MSG2---------|------MSG3------------|

  |START|DATA|------|START|DATA|---|START|DATA|STOP|      

If my commit text does not make this clear, I  can reword that ?

Regards,
  Sricharan

[toc] | [next] | [standalone]

#1327150 — Re: [PATCH V7 3/6] i2c: qup: Transfer each i2c_msg in i2c_msgs without a stop bit

[Multipart message — attachments visible in raw view] — view raw

Hi,

> Ah, so what I meant above is there is no 'STOP' bit between each msg in
> i2c_msgs,
> but 'REAPEATED_START' still holds true.  We are sending 'START' bit for each
> msg.
> So these is how each msg in i2c_msg is sent,
>
> |------MSG1--------|-----MSG2---------|------MSG3------------|
>
>   |START|DATA|------|START|DATA|---|START|DATA|STOP|
>
> If my commit text does not make this clear, I  can reword that ?

OK, now this looks to me perfectly fine: A number of *messages*
concatenated into one *transfer* by repeated start. That's the way it
should be.

So, I'd simply remove these words:

"The QUP i2c hardware has no way to inform that there should not be a
'STOP' at the end of transaction. The only way to implement this is to
coalesce all the i2c_msg in i2c_msgs in to one transaction and transfer
them."

This sounded like the HW needed a special handling, so I was under the
impression REP_START was broken. However, unless I misunderstood
something again, this now sounds like the standard case and we can keep
the commit message simple. If you are okay with that, I can update it
here, no need to resend.

Thanks,

   Wolfram

[toc] | [prev] | [next] | [standalone]

#1327525

Hi Wolfram,

> -----Original Message-----
> From: linux-arm-kernel [mailto:linux-arm-kernel-
> bounces@lists.infradead.org] On Behalf Of Wolfram Sang
> Sent: Friday, February 05, 2016 1:39 AM
> To: Sricharan
> Cc: devicetree@vger.kernel.org; architt@codeaurora.org; linux-arm-
> msm@vger.kernel.org; ntelkar@codeaurora.org; galak@codeaurora.org;
> linux-kernel@vger.kernel.org; andy.gross@linaro.org; linux-
> i2c@vger.kernel.org; iivanov@mm-sol.com; agross@codeaurora.org;
> dmaengine@vger.kernel.org; linux-arm-kernel@lists.infradead.org
> Subject: Re: [PATCH V7 3/6] i2c: qup: Transfer each i2c_msg in i2c_msgs
> without a stop bit
> 
> Hi,
> 
> > Ah, so what I meant above is there is no 'STOP' bit between each msg
> > in i2c_msgs, but 'REAPEATED_START' still holds true.  We are sending
> > 'START' bit for each msg.
> > So these is how each msg in i2c_msg is sent,
> >
> > |------MSG1--------|-----MSG2---------|------MSG3------------|
> >
> >   |START|DATA|------|START|DATA|---|START|DATA|STOP|
> >
> > If my commit text does not make this clear, I  can reword that ?
> 
> OK, now this looks to me perfectly fine: A number of *messages*
> concatenated into one *transfer* by repeated start. That's the way it
should
> be.
> 
> So, I'd simply remove these words:
> 
> "The QUP i2c hardware has no way to inform that there should not be a
> 'STOP' at the end of transaction. The only way to implement this is to
> coalesce all the i2c_msg in i2c_msgs in to one transaction and transfer
them."
> 
> This sounded like the HW needed a special handling, so I was under the
> impression REP_START was broken. However, unless I misunderstood
> something again, this now sounds like the standard case and we can keep
> the commit message simple. If you are okay with that, I can update it
here,
> no need to resend.
> 
      Yes the above modified commit text looks perfect to be updated and
thanks
      for the update as well.

Regards,
 Sricharan

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web