linux-kernel - Re: [PATCH v3 3/6] spi: sun6i: restrict transfer length in PIO-mode

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Message-ID: <ee4adb1e-caf6-32f6-33d6-d8dd94d232cf@orpaltech.com>
Date:   Thu, 5 Apr 2018 12:59:35 +0300
From:   Sergey Suloev <ssuloev@...altech.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Chen-Yu Tsai <wens@...e.org>, Mark Brown <broonie@...nel.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-spi@...r.kernel.org
Subject: Re: [PATCH v3 3/6] spi: sun6i: restrict transfer length in PIO-mode

On 04/05/2018 12:19 PM, Maxime Ripard wrote:
> On Wed, Apr 04, 2018 at 02:35:14PM +0300, Sergey Suloev wrote:
>> On 04/04/2018 09:50 AM, Maxime Ripard wrote:
>>> On Tue, Apr 03, 2018 at 06:44:46PM +0300, Sergey Suloev wrote:
>>>> There is no need to handle 3/4 empty interrupt as the maximum
>>>> supported transfer length in PIO mode is equal to FIFO depth,
>>>> i.e. 128 bytes for sun6i and 64 bytes for sun8i SoCs.
>>>>
>>>> Changes in v3:
>>>> 1) Restored processing of 3/4 FIFO full interrupt.
>>>>
>>>> Signed-off-by: Sergey Suloev <ssuloev@...altech.com>
>>>> ---
>>>>    drivers/spi/spi-sun6i.c | 41 +++++++++++++++++------------------------
>>>>    1 file changed, 17 insertions(+), 24 deletions(-)
>>>>
>>>> diff --git a/drivers/spi/spi-sun6i.c b/drivers/spi/spi-sun6i.c
>>>> index 78acc1f..c09ad10 100644
>>>> --- a/drivers/spi/spi-sun6i.c
>>>> +++ b/drivers/spi/spi-sun6i.c
>>>> @@ -207,7 +207,10 @@ static void sun6i_spi_set_cs(struct spi_device *spi, bool enable)
>>>>    static size_t sun6i_spi_max_transfer_size(struct spi_device *spi)
>>>>    {
>>>> -	return SUN6I_MAX_XFER_SIZE - 1;
>>>> +	struct spi_master *master = spi->master;
>>>> +	struct sun6i_spi *sspi = spi_master_get_devdata(master);
>>>> +
>>>> +	return sspi->fifo_depth;
>>> Doesn't that effectively revert 3288d5cb40c0 ?
>>>
>>> Why do you need to do so?
>> Need what?
> Why do you need to revert that change.
>
>> Change is supposed to restrict max transfer size for PIO mode otherwise it
>> will fail.
>> The maximum transfer length = FIFO depth for PIO mode.
> The point of that patch was precisely to allow to send more data than
> the FIFO. You're breaking that behaviour without any justification,
> and this is not ok.

I am sorry, but you can't. That's a hardware limitation.
>>>>    }
>>>>    static int sun6i_spi_prepare_message(struct spi_master *master,
>>>> @@ -255,8 +258,14 @@ static int sun6i_spi_transfer_one(struct spi_master *master,
>>>>    	int ret = 0;
>>>>    	u32 reg;
>>>> -	if (tfr->len > SUN6I_MAX_XFER_SIZE)
>>>> -		return -EINVAL;
>>>> +	/* A zero length transfer never finishes if programmed
>>>> +	   in the hardware */
>>> Improper comment style here. Please make sure to run checkpatch before
>>> sending your patches.
>> ok
>>>> +	if (!tfr->len)
>>>> +		return 0;
>>> Can that case even happen?
>> Not sure, just for safety.
>>>> +	/* Don't support transfer larger than the FIFO */
>>>> +	if (tfr->len > sspi->fifo_depth)
>>>> +		return -EMSGSIZE;
>>> You're changing the return type, why?
>> As  a more appropriate one
> The fact that it's more appropriate should be justified.
>
>>>>    	reinit_completion(&sspi->done);
>>>>    	sspi->tx_buf = tfr->tx_buf;
>>>> @@ -278,8 +287,7 @@ static int sun6i_spi_transfer_one(struct spi_master *master,
>>>>    	 */
>>>>    	trig_level = sspi->fifo_depth / 4 * 3;
>>>>    	sun6i_spi_write(sspi, SUN6I_FIFO_CTL_REG,
>>>> -			(trig_level << SUN6I_FIFO_CTL_RF_RDY_TRIG_LEVEL_BITS) |
>>>> -			(trig_level << SUN6I_FIFO_CTL_TF_ERQ_TRIG_LEVEL_BITS));
>>>> +			(trig_level << SUN6I_FIFO_CTL_RF_RDY_TRIG_LEVEL_BITS));
>>>>    	reg = sun6i_spi_read(sspi, SUN6I_TFR_CTL_REG);
>>>> @@ -343,11 +351,8 @@ static int sun6i_spi_transfer_one(struct spi_master *master,
>>>>    	sun6i_spi_fill_fifo(sspi, sspi->fifo_depth);
>>>>    	/* Enable the interrupts */
>>>> -	sun6i_spi_write(sspi, SUN6I_INT_CTL_REG, SUN6I_INT_CTL_TC);
>>>>    	sun6i_spi_enable_interrupt(sspi, SUN6I_INT_CTL_TC |
>>>>    					 SUN6I_INT_CTL_RF_RDY);
>>>> -	if (tx_len > sspi->fifo_depth)
>>>> -		sun6i_spi_enable_interrupt(sspi, SUN6I_INT_CTL_TF_ERQ);
>>> This would also need to be explained in your commit log.
>> What exactly and in what way ?
> You should explain, at least:
> A) What is the current behaviour
> B) Why that is a problem, or what problem does it cause
> C) What solution you implement and why you think it's justified
>
>>>>    	/* Start the transfer */
>>>>    	reg = sun6i_spi_read(sspi, SUN6I_TFR_CTL_REG);
>>>> @@ -376,7 +381,9 @@ out:
>>>>    static irqreturn_t sun6i_spi_handler(int irq, void *dev_id)
>>>>    {
>>>>    	struct sun6i_spi *sspi = dev_id;
>>>> -	u32 status = sun6i_spi_read(sspi, SUN6I_INT_STA_REG);
>>>> +	u32 status;
>>>> +
>>>> +	status = sun6i_spi_read(sspi, SUN6I_INT_STA_REG);
>>> Why is this change needed?
>> A minor one, for readability.
> That's arguable, and you should have a single logical change per
> patch. So this doesn't belong in this one.
>
> Maxime
>
>
>
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> linux-arm-kernel@...ts.infradead.org
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