[U-Boot] [PATCH 1/2] spi: ti_qspi: Add dummy readl for bus sync

[Jagan Teki]

On 17 November 2015 at 11:57, Vignesh R <vigneshr at ti.com> wrote:
>
>
> On 11/17/2015 11:33 AM, Jagan Teki wrote:
>> On 10 November 2015 at 11:52, Vignesh R <vigneshr at ti.com> wrote:
>>> Add dummy readl after invalidating cmd field of QSPI_CMD_REG to ensure
>>> bus sync. Without this device's CS is not deactivated reliably leading
>>> to failure to enumerate flash or failure to set quad enable bit on
>>> Macronix flash present on am437x-sk and am437x-idk evms.
>>>
>>> Signed-off-by: Vignesh R <vigneshr at ti.com>
>>> ---
>>>  drivers/spi/ti_qspi.c | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/drivers/spi/ti_qspi.c b/drivers/spi/ti_qspi.c
>>> index bd63db8a2acc..ba2da017c21a 100644
>>> --- a/drivers/spi/ti_qspi.c
>>> +++ b/drivers/spi/ti_qspi.c
>>> @@ -170,6 +170,8 @@ void spi_cs_deactivate(struct spi_slave *slave)
>>>         debug("spi_cs_deactivate: 0x%08x\n", (u32)slave);
>>>
>>>         writel(qslave->cmd | QSPI_INVAL, &qslave->base->cmd);
>>> +       /* dummy readl to ensure bus sync */
>>> +       readl(&qslave->base->cmd);
>>
>> Isn't effect anything for non-quad case? and dummy bytes might changed
>> based on quad and quadio does this single dummy readl is same for
>> those cases as well?
>
> No, this dummy readl is not related as dummy bytes used in QUAD mode.
>
> In ti_qspi controller, in order to end a read/write request (ie to
> deassert ChipSelect) invalid cmd(0x4) needs to be written to CMD field
> of QSPI_CMD_REG (which is done by above function) in all modes.
> Sometimes, this write may have been flushed out of ARM but may not have
> reached the QSPI IP yet (ie bus/interconnect is not flushed yet) hence
> ChipSelect is not deactivated. Therefore, the successive write/read
> operation may overlaps resulting in wrong data being read from flash.
> Reading back QSPI_CMD_REG makes sure that the bus/interconnect is
> flushed and register write is affected making sure CS is deactivated.

Thanks for the info.

Reviewed-by: Jagan Teki <jteki at openedev.com>

-- 
Jagan.