[PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Sergey Suloev]

On 04/03/2018 02:40 PM, Maxime Ripard wrote:
> On Tue, Apr 03, 2018 at 02:08:43PM +0300, Sergey Suloev wrote:
>> On 04/03/2018 11:10 AM, Maxime Ripard wrote:
>>> On Thu, Mar 29, 2018 at 09:59:03PM +0300, Sergey Suloev wrote:
>>>> There is no need to handle 3/4 empty/full interrupts as the maximum
>>>> supported transfer length in PIO mode is 64 bytes for sun4i-family
>>>> SoCs.
>>> That assumes that you'll be able to treat the FIFO full interrupt and
>>> drain the FIFO before we have the next byte coming in. This would
>>> require a real time system, and we're not in one of them.
>> AFAIK in SPI protocol we send and receive at the same time.
> It depends. The protocol allows it yes, but most devices I've seen can
> only operate in half duplex. But it's not really the point.
>
>> As soon as the transfer length is <= FIFO depth then it means that
>> at the moment we get TC interrupt all data for this transfer
>> sent/received already.
>>
>> Is your point here that draining FIFO might be a long operation and we can
>> lose next portion of data ?
> My point is that, if you get another interrupt(s) right before the
> FIFO full interrupt, that interrupt is going to be masked for as long
> as it is needed for the previous handler(s) to execute.
>
> If you're having another byte received while the interrupt is masked,
> you're losing data.
>
> Maxime
>
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

ok, I am going to put back 3/4 full handler then.