linux-kernel - Re: [PATCH v5 2/4] dmaengine: gpi: Add Lock and Unlock TRE support to access I2C exclusively

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Message-ID: <1566eafb-7286-4f27-922d-0bbaaab8120b@quicinc.com>
Date: Tue, 14 Jan 2025 14:48:01 +0530
From: Mukesh Kumar Savaliya <quic_msavaliy@...cinc.com>
To: Vinod Koul <vkoul@...nel.org>, Md Sadre Alam <quic_mdalam@...cinc.com>
CC: <konrad.dybcio@...aro.org>, <andersson@...nel.org>,
        <andi.shyti@...nel.org>, <linux-arm-msm@...r.kernel.org>,
        <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-i2c@...r.kernel.org>, <conor+dt@...nel.org>,
        <agross@...nel.org>, <devicetree@...r.kernel.org>, <linux@...blig.org>,
        <dan.carpenter@...aro.org>, <Frank.Li@....com>,
        <konradybcio@...nel.org>, <bryan.odonoghue@...aro.org>,
        <krzk+dt@...nel.org>, <robh@...nel.org>, <quic_vdadhani@...cinc.com>
Subject: Re: [PATCH v5 2/4] dmaengine: gpi: Add Lock and Unlock TRE support to
 access I2C exclusively

Hi Vinod,

On 12/26/2024 5:52 PM, Mukesh Kumar Savaliya wrote:
> 
> 
> On 12/24/2024 3:28 PM, Vinod Koul wrote:
>> On 18-12-24, 18:04, Mukesh Kumar Savaliya wrote:
>>> Hi Vinod, Thanks !  I just saw your comments now as somehow it was 
>>> going in
>>> some other folder and didn't realize.
>>>
>>> On 12/4/2024 5:51 PM, Vinod Koul wrote:
>>>> On 02-12-24, 16:13, Mukesh Kumar Savaliya wrote:
>>>>> Thanks for the review comments Vinod !
>>>>>
>>>>> On 12/2/2024 12:17 PM, Vinod Koul wrote:
>>>>>> On 29-11-24, 20:13, Mukesh Kumar Savaliya wrote:
>>>>>>> GSI DMA provides specific TREs(Transfer ring element) namely Lock 
>>>>>>> and
>>>>>>> Unlock TRE. It provides mutually exclusive access to I2C 
>>>>>>> controller from
>>>>>>> any of the processor(Apps,ADSP). Lock prevents other subsystems from
>>>>>>> concurrently performing DMA transfers and avoids disturbance to 
>>>>>>> data path.
>>>>>>> Basically for shared I2C usecase, lock the SE(Serial Engine) for 
>>>>>>> one of
>>>>>>> the processor, complete the transfer, unlock the SE.
>>>>>>>
>>>>>>> Apply Lock TRE for the first transfer of shared SE and Apply Unlock
>>>>>>> TRE for the last transfer.
>>>>>>>
>>>>>>> Also change MAX_TRE macro to 5 from 3 because of the two 
>>>>>>> additional TREs.
>>>>>>>
>>>>>>
>>>>>> ...
>>>>>>
>>>>>>> @@ -65,6 +65,9 @@ enum i2c_op {
>>>>>>>      * @rx_len: receive length for buffer
>>>>>>>      * @op: i2c cmd
>>>>>>>      * @muli-msg: is part of multi i2c r-w msgs
>>>>>>> + * @shared_se: bus is shared between subsystems
>>>>>>> + * @bool first_msg: use it for tracking multimessage xfer
>>>>>>> + * @bool last_msg: use it for tracking multimessage xfer
>>>>>>>      */
>>>>>>>     struct gpi_i2c_config {
>>>>>>>         u8 set_config;
>>>>>>> @@ -78,6 +81,9 @@ struct gpi_i2c_config {
>>>>>>>         u32 rx_len;
>>>>>>>         enum i2c_op op;
>>>>>>>         bool multi_msg;
>>>>>>> +    bool shared_se;
>>>>>>
>>>>>> Looking at this why do you need this field? It can be internal to 
>>>>>> your
>>>>>> i2c driver... Why not just set an enum for lock and use the values as
>>>>>> lock/unlock/dont care and make the interface simpler. I see no 
>>>>>> reason to
>>>>>> use three variables to communicate the info which can be handled in
>>>>>> simpler way..?
>>>>>>
>>>>> Below was earlier reply to [PATCH V3, 2/4], please let me know if 
>>>>> you have
>>>>> any additional comment and need further clarifications.
>>>>
>>>> Looks like you misunderstood, the question is why do you need three
>>>> variables to convey this info..? Use a single variable please
>>> Yes, I think so. Please let me clarify.
>>> First variable is a feature flag and it's required to be explicitly
>>> mentioned by client (i2c/spi/etc) to GSI driver.
>>>
>>> Second and third, can be optimized to boolean so either first or last 
>>> can be
>>> passed.
>>>
>>> Please correct me or add simple change where you would like to make, 
>>> i can
>>> add that.
>>
>> I though we could do with a single and derive
>>
> Sure, so as mentioned in the other crypto BAM patch probably dmaengine.h 
> can hold flag and that can add support for lock/unlock similar to that 
> patch.
> I just realized it from your shared patch. let me work internally with 
> Md sadre and review. Thanks for the comment.
>> Also, please see 20241212041639.4109039-3-quic_mdalam@...cinc.com, folks
>> from same company should talk together on same solutions, please
>> converge and come up with a single proposal which works for both drivers
>>
I have discussed with Md Sadre and tried to understand and utilize the 
enum of lock and unlock in my changes. Below is the summary.

I can't use those lock and unlock enums here because it's required for 
first and last message respectively. intermediate transfers will not use 
anything. So we need to define one more enum like dma_ctrl_none.

if i create another internal parent structure having required 3 members, 
then also it will need 3 child members. So i think current one looks 
good to me.

Please help review and suggest if anything can be better here.

> Sure
> 
>