[PATCH] i2c: aspeed: fix master pending state handling

Tao Ren taoren at fb.com
Fri Oct 11 10:11:36 AEDT 2019

On 10/10/19 3:04 PM, Jae Hyun Yoo wrote:
> On 10/10/2019 2:20 PM, Tao Ren wrote:
>> On 10/9/19 2:20 PM, Jae Hyun Yoo wrote:
> [...]
>>>           /*
>>>            * If a peer master starts a xfer immediately after it queues a
>>> -         * master command, change its state to 'pending' then H/W will
>>> -         * continue the queued master xfer just after completing the
>>> -         * slave mode session.
>>> +         * master command, clear the queued master command and change
>>> +         * its state to 'pending'. To simplify handling of pending
>>> +         * cases, it uses S/W solution instead of H/W command queue
>>> +         * handling.
>>>            */
>>>           if (unlikely(irq_status & ASPEED_I2CD_INTR_SLAVE_MATCH)) {
>>> +            writel(readl(bus->base + ASPEED_I2C_CMD_REG) &
>>> +                ~ASPEED_I2CD_MASTER_CMDS_MASK,
>>> +                   bus->base + ASPEED_I2C_CMD_REG);
>> Sorry for the late comments (just noticed this line while testing the patch):
>> I assume this line is aimed at stopping the running master commands, but as per
>> AST2500 datasheet, it's NOP to write 0 to MASTER_STOP/MASTER_RX/MASTER_TX bits.
>> Maybe all we need is writing 1 to MASTER_STOP field?
> There could be two pending cases:
> 1. Master goes to pending before it triggers a command if a slave
>    operation is already initiated.
> 2. Master goes to pending after it triggered a command if a peer
>    master immediately sends something just after the master command
>    triggering.
> Above code is for the latter case. H/W handles the case priority based
> so the slave event will be handled first, and then the master command
> will be handled when the slave operation is completed. Problem is,
> this H/W shares the same buffer for master and slave operations so
> it's unreliable. Above code just removes the master command from the
> command register to prevent this H/W command handling of pending events.
> Instead, it restarts the master command using a call of aspeed_i2c_do_start when the slave operation is completed.

Thanks for the clarify, Jae. I mean clearing these bits has no effect to
hardware according to aspeed datasheet; in other word, master command cannot
be removed from command register by this statement.

For example, below is the description for MASTER_STOP_CMD(I2CD14, bit 5):

  0: NOP
  1: Issue Master Stop Command
  This register will be automatically cleared by H/W when Stop Command has
  been issues.



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