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.
Cheers,
Tao
