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

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Message-ID: <4390604e-092b-a89d-3581-b57ee9cbb6a1@orpaltech.com>
Date:   Tue, 3 Apr 2018 14:08:43 +0300
From:   Sergey Suloev <ssuloev@...altech.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Mark Brown <broonie@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        linux-spi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

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.
>
> Maxime
>
AFAIK in SPI protocol we send and receive at the same time. 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 ?