linux-kernel - Re: [V3] i2c: i2c-qcom-geni: Correct I2C TRE sequence

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Message-ID: <aa7a28a7-59c6-4783-a6de-9a46721a8bf6@linaro.org>
Date: Fri, 9 Feb 2024 15:41:43 +0100
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Andi Shyti <andi.shyti@...nel.org>,
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Viken Dadhaniya <quic_vdadhani@...cinc.com>, andersson@...nel.org,
 linux-arm-msm@...r.kernel.org, linux-i2c@...r.kernel.org,
 linux-kernel@...r.kernel.org, vkoul@...nel.org, quic_bjorande@...cinc.com,
 manivannan.sadhasivam@...aro.org, bryan.odonoghue@...aro.org,
 quic_msavaliy@...cinc.com, quic_vtanuku@...cinc.com
Subject: Re: [V3] i2c: i2c-qcom-geni: Correct I2C TRE sequence

On 8.02.2024 12:59, Andi Shyti wrote:
> Hi Dmitry,
> 
> On Thu, Feb 08, 2024 at 01:04:14PM +0200, Dmitry Baryshkov wrote:
>> On Thu, 8 Feb 2024 at 12:02, Andi Shyti <andi.shyti@...nel.org> wrote:
>>>
>>> Hi Viken, Dmitry,
>>>
>>> On Fri, Feb 02, 2024 at 04:13:06PM +0530, Viken Dadhaniya wrote:
>>>>
>>>> On 2/1/2024 5:24 PM, Dmitry Baryshkov wrote:
>>>>> On Thu, 1 Feb 2024 at 12:13, Viken Dadhaniya <quic_vdadhani@...cinc.com> wrote:
>>>>>>
>>>>>> For i2c read operation in GSI mode, we are getting timeout
>>>>>> due to malformed TRE basically incorrect TRE sequence
>>>>>> in gpi(drivers/dma/qcom/gpi.c) driver.
>>>>>>
>>>>>> TRE stands for Transfer Ring Element - which is basically an element with
>>>>>> size of 4 words. It contains all information like slave address,
>>>>>> clk divider, dma address value data size etc).
>>>>>>
>>>>>> Mainly we have 3 TREs(Config, GO and DMA tre).
>>>>>> - CONFIG TRE : consists of internal register configuration which is
>>>>>>                 required before start of the transfer.
>>>>>> - DMA TRE :    contains DDR/Memory address, called as DMA descriptor.
>>>>>> - GO TRE :     contains Transfer directions, slave ID, Delay flags, Length
>>>>>>                 of the transfer.
>>>>>>
>>>>>> Driver calls GPI driver API to config each TRE depending on the protocol.
>>>>>> If we see GPI driver, for RX operation we are configuring DMA tre and
>>>>>> for TX operation we are configuring GO tre.
>>>>>>
>>>>>> For read operation tre sequence will be as below which is not aligned
>>>>>> to hardware programming guide.
>>>>>>
>>>>>> - CONFIG tre
>>>>>> - DMA tre
>>>>>> - GO tre
>>>>>>
>>>>>> As per Qualcomm's internal Hardware Programming Guide, we should configure
>>>>>> TREs in below sequence for any RX only transfer.
>>>>>>
>>>>>> - CONFIG tre
>>>>>> - GO tre
>>>>>> - DMA tre
>>>>>>
>>>>>> In summary, for RX only transfers, we are reordering DMA and GO TREs.
>>>>>> Tested covering i2c read/write transfer on QCM6490 RB3 board.
>>>>>
>>>>> This hasn't improved. You must describe what is the connection between
>>>>> TRE types and the geni_i2c_gpi calls.
>>>>> It is not obvious until somebody looks into the GPI DMA driver.
>>>>>
>>>>> Another point, for some reason you are still using just the patch
>>>>> version in email subject. Please fix your setup so that the email
>>>>> subject also includes the `[PATCH` part in the subject, which is there
>>>>> by default.
>>>>> Hint: git format-patch -1 -v4 will do that for you without a need to
>>>>> correct anything afterwards.
>>>>>
>>>>
>>>> At high level, let me explain the I2C to GPI driver flow in general.
>>>>
>>>> I2C driver calls GPI driver exposed functions which will prepare all the
>>>> TREs as per programming guide and
>>>> queues to the GPI DMA engine for execution. Upon completion of the Transfer,
>>>> GPI DMA engine will generate an
>>>> interrupt which will be handled inside the GPIO driver. Then GPI driver will
>>>> call DMA framework registered callback by i2c.
>>>> Upon receiving this callback, i2c driver marks the transfer completion.
>>>
>>> Any news about this? Dmitry do you still have concerns? We can
>>> add this last description in the commit log, as well, if needed.
>>
>> I was looking for pretty simple addition to the commit message, that
>> links existing commit message to the actual source code change: that
>> geni_i2c_gpi(I2C_WRITE) results in the GO TRE and
>> geni_i2c_gpi(I2C_READ) generates DMA TRE. But I haven't seen anything
>> sensible up to now. So far we have a nice description of required
>> programming sequence in terms of CONFIG, GO, DMA TREs and then source
>> code change that seems completely unrelated to the commit message,
>> unless one actually goes deep into the corresponding GPI DMA driver.
> 
> Agree. I can't take this patch until the commit message has a
> proper description and until Dmitry doesn't have any concerns
> pending.

And please, please, include the word PATCH in the square brackets in
the subject, it's landing in the wrong email folders for a number of
folks..

Konrad