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: <d49b16b2-95e5-42b4-9bc1-40cb0bfa15b1@quicinc.com>
Date: Mon, 2 Dec 2024 16:13:59 +0530
From: Mukesh Kumar Savaliya <quic_msavaliy@...cinc.com>
To: Vinod Koul <vkoul@...nel.org>
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

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.
--
 > Looking at the usage in following patches, why cant this be handled
 > internally as part of prep call?
 >
As per design, i2c driver iterates over each message and submits to GPI 
where it creates TRE. Since it's per transfer, we need to create Lock 
and Unlock TRE based on first or last message.
--
>> +	bool first_msg;
>> +	bool last_msg;
>