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

Jae Hyun Yoo
2019-10-10T22:04:00Z

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,

Jae