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SubjectRe: [PATCH] i2c: aspeed: Improve driver to support multi-master use cases stably
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Hi Jarkko,

Thanks for the review. Please see my answer below.

On 6/27/2018 12:48 AM, Jarkko Nikula wrote:
> Hi
>
> On 06/26/2018 07:58 PM, Jae Hyun Yoo wrote:
>> BMC firmware should support some multi-master use cases such as
>> multi-node,
>> IPMB, BMC-ME link and so on but the current ASPEED I2C driver is a bit
>> unstable for the multi-master use case. So this patch improves ASPEED I2C
>> driver to support the multi-master use case stably.
>>
>> Changes:
>> * Added XFER_MODE status register checking logic into
>>    aspeed_i2c_master_xfer to improve the current bus busy checking logic.
>> * Changed the order of enum aspeed_i2c_master_state and
>>    enum aspeed_i2c_slave_state defines to make their initial values
>> set to
>>    ASPEED_I2C_MASTER_INACTIVE and ASPEED_I2C_SLAVE_STOP respectively.
>>    In case of multi-master use with previous code, if a slave data comes
>>    ahead of the first master xfer, master_state starts from an invalid
>>    state. This change fixed the issue.
>> * Adjusted spin_lock scope to make it wrap the whole irq handler using
>>    a single lock and unlock pair covers both master and slave handlers.
>> * Added irq_status variable as a member of the struct aspeed_i2c_bus to
>>    collect handled interrupt bits throughout the master and the slave irq
>>    handlers.
>> * Added control logic to put an order on calling the master and the slave
>>    irq handlers based on their current states.
>>
> This does many unrelated looking changes in one patch making it more
> vulnerable for potential multiple regressions. For instance busy
> checking goes from single read to loop with 250 ms timeout in this patch
> while changing also spin lock logic and interrupt handling.
>
> Now if there is some regression it might be difficult to find what
> change in this patch is causing it and more over things goes more
> complicated if some other kind of regressions are found pointing into
> the same commit.
>
> I suggest splitting this into multiple smaller patches. For instance
> having first simple conversions patches that are unlikely to cause a
> regression like one patch adding '\n' to error print, another moving
> irq_status variable into struct aspeed_i2c_bus and so on followed by
> patches that change logic like busy checking, spin lock change and then
> patch or more for multi-master support.
>

Yes, that makes sense and I agree with you. I'll split out this patch
into multiple smaller patches as you suggested.

Thanks,

Jae

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