Re: [linux-sunxi] [PATCH 1/5] spi: sunxi: fix transfer timeout

Re: [linux-sunxi] [PATCH 1/5] spi: sunxi: fix transfer timeout

[Julian Calaby]

Hi Michal,

On Fri, May 27, 2016 at 5:25 AM, Michal Suchanek <hramrach@gmail.com> wrote:
> The trasfer timeout is fixed at 1000 ms. Reading a 4Mbyte flash over
> 1MHz SPI bus takes way longer than that. Calculate the timeout from the
> actual time the transfer is supposed to take and multiply by 2 for good
> measure.
>
> Signed-off-by: Michal Suchanek <hramrach@gmail.com>
> ---
>
> v2:
> - fix build error
> - use unsigned instead of int in max_t
> - use tfr->speed_hz instead of sspi->max_speed_hz
> ---
>  drivers/spi/spi-sun4i.c | 11 ++++++++++-
>  drivers/spi/spi-sun6i.c | 11 ++++++++++-
>  2 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
> index 1ddd9e2..fe63bbd 100644
> --- a/drivers/spi/spi-sun4i.c
> +++ b/drivers/spi/spi-sun4i.c
> @@ -173,6 +173,7 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
>  {
>         struct sun4i_spi *sspi = spi_master_get_devdata(master);
>         unsigned int mclk_rate, div, timeout;
> +       unsigned int start, end, tx_time;
>         unsigned int tx_len = 0;
>         int ret = 0;
>         u32 reg;
> @@ -279,9 +280,17 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
>         reg = sun4i_spi_read(sspi, SUN4I_CTL_REG);
>         sun4i_spi_write(sspi, SUN4I_CTL_REG, reg | SUN4I_CTL_XCH);
>
> +       tx_time = max_t(unsigned, tfr->len * 8 * 2 / (tfr->speed_hz / 1000),

You should probably use "unsigned int" instead of just "unsigned" here.

> +                       100);
> +       start = jiffies;
>         timeout = wait_for_completion_timeout(&sspi->done,
> -                                             msecs_to_jiffies(1000));
> +                                             msecs_to_jiffies(tx_time));
> +       end = jiffies;
>         if (!timeout) {
> +               dev_warn(&master->dev,
> +                        "%s: timeout transferring %u bytes@%iHz for %i(%i)ms",
> +                        dev_name(&spi->dev), tfr->len, tfr->speed_hz,
> +                        jiffies_to_msecs(end - start), tx_time);

Should the debug changes be in a separate patch?

>                 ret = -ETIMEDOUT;
>                 goto out;
>         }
> diff --git a/drivers/spi/spi-sun6i.c b/drivers/spi/spi-sun6i.c
> index 42e2c4b..8be5c5c 100644
> --- a/drivers/spi/spi-sun6i.c
> +++ b/drivers/spi/spi-sun6i.c
> @@ -162,6 +162,7 @@ static int sun6i_spi_transfer_one(struct spi_master *master,
>         unsigned int mclk_rate, div, timeout;
>         unsigned int tx_len = 0;
>         int ret = 0;
> +       unsigned int start, end, tx_time;
>         u32 reg;
>
>         /* We don't support transfer larger than the FIFO */
> @@ -269,9 +270,17 @@ static int sun6i_spi_transfer_one(struct spi_master *master,
>         reg = sun6i_spi_read(sspi, SUN6I_TFR_CTL_REG);
>         sun6i_spi_write(sspi, SUN6I_TFR_CTL_REG, reg | SUN6I_TFR_CTL_XCH);
>
> +       tx_time = max_t(unsigned, tfr->len * 8 * 2 / (tfr->speed_hz / 1000),

Ditto, "unsigned int" instead of "unsigned"?

> +                       100);
> +       start = jiffies;
>         timeout = wait_for_completion_timeout(&sspi->done,
> -                                             msecs_to_jiffies(1000));
> +                                             msecs_to_jiffies(tx_time));
> +       end = jiffies;
>         if (!timeout) {
> +               dev_warn(&master->dev,
> +                        "%s: timeout transferring %u bytes@%iHz for %i(%i)ms",
> +                        dev_name(&spi->dev), tfr->len, tfr->speed_hz,
> +                        jiffies_to_msecs(end - start), tx_time);

Ditto, separate patch?

Also, should the changes for the drivers be in two separate patches also?

Thanks,

-- 
Julian Calaby

Email: julian.calaby@gmail.com
Profile: http://www.google.com/profiles/julian.calaby/

Re: [linux-sunxi] [PATCH 1/5] spi: sunxi: fix transfer timeout

[Michal Suchanek]

On 27 May 2016 at 04:05, Julian Calaby <julian.calaby@gmail.com> wrote:
> Hi Michal,
>
> On Fri, May 27, 2016 at 5:25 AM, Michal Suchanek <hramrach@gmail.com> wrote:
>> The trasfer timeout is fixed at 1000 ms. Reading a 4Mbyte flash over
>> 1MHz SPI bus takes way longer than that. Calculate the timeout from the
>> actual time the transfer is supposed to take and multiply by 2 for good
>> measure.
>>
>> Signed-off-by: Michal Suchanek <hramrach@gmail.com>
>> ---
>>
>> v2:
>> - fix build error
>> - use unsigned instead of int in max_t
>> - use tfr->speed_hz instead of sspi->max_speed_hz
>> ---
>>  drivers/spi/spi-sun4i.c | 11 ++++++++++-
>>  drivers/spi/spi-sun6i.c | 11 ++++++++++-
>>  2 files changed, 20 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
>> index 1ddd9e2..fe63bbd 100644
>> --- a/drivers/spi/spi-sun4i.c
>> +++ b/drivers/spi/spi-sun4i.c
>> @@ -173,6 +173,7 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
>>  {
>>         struct sun4i_spi *sspi = spi_master_get_devdata(master);
>>         unsigned int mclk_rate, div, timeout;
>> +       unsigned int start, end, tx_time;
>>         unsigned int tx_len = 0;
>>         int ret = 0;
>>         u32 reg;
>> @@ -279,9 +280,17 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
>>         reg = sun4i_spi_read(sspi, SUN4I_CTL_REG);
>>         sun4i_spi_write(sspi, SUN4I_CTL_REG, reg | SUN4I_CTL_XCH);
>>
>> +       tx_time = max_t(unsigned, tfr->len * 8 * 2 / (tfr->speed_hz / 1000),
>
> You should probably use "unsigned int" instead of just "unsigned" here.
>
>> +                       100);

Or just 100U constant and avoid max_t altogether.

>> +       start = jiffies;
>>         timeout = wait_for_completion_timeout(&sspi->done,
>> -                                             msecs_to_jiffies(1000));
>> +                                             msecs_to_jiffies(tx_time));
>> +       end = jiffies;
>>         if (!timeout) {
>> +               dev_warn(&master->dev,
>> +                        "%s: timeout transferring %u bytes@%iHz for %i(%i)ms",
>> +                        dev_name(&spi->dev), tfr->len, tfr->speed_hz,
>> +                        jiffies_to_msecs(end - start), tx_time);
>
> Should the debug changes be in a separate patch?

Is this so big of a change that it needs to be split?

>
>>                 ret = -ETIMEDOUT;
>>                 goto out;
>>         }
>> diff --git a/drivers/spi/spi-sun6i.c b/drivers/spi/spi-sun6i.c
>> index 42e2c4b..8be5c5c 100644
>> --- a/drivers/spi/spi-sun6i.c
>> +++ b/drivers/spi/spi-sun6i.c
>> @@ -162,6 +162,7 @@ static int sun6i_spi_transfer_one(struct spi_master *master,
>>         unsigned int mclk_rate, div, timeout;
>>         unsigned int tx_len = 0;
>>         int ret = 0;
>> +       unsigned int start, end, tx_time;
>>         u32 reg;
>>
>>         /* We don't support transfer larger than the FIFO */
>> @@ -269,9 +270,17 @@ static int sun6i_spi_transfer_one(struct spi_master *master,
>>         reg = sun6i_spi_read(sspi, SUN6I_TFR_CTL_REG);
>>         sun6i_spi_write(sspi, SUN6I_TFR_CTL_REG, reg | SUN6I_TFR_CTL_XCH);
>>
>> +       tx_time = max_t(unsigned, tfr->len * 8 * 2 / (tfr->speed_hz / 1000),
>
> Ditto, "unsigned int" instead of "unsigned"?
>
>> +                       100);
>> +       start = jiffies;
>>         timeout = wait_for_completion_timeout(&sspi->done,
>> -                                             msecs_to_jiffies(1000));
>> +                                             msecs_to_jiffies(tx_time));
>> +       end = jiffies;
>>         if (!timeout) {
>> +               dev_warn(&master->dev,
>> +                        "%s: timeout transferring %u bytes@%iHz for %i(%i)ms",
>> +                        dev_name(&spi->dev), tfr->len, tfr->speed_hz,
>> +                        jiffies_to_msecs(end - start), tx_time);
>
> Ditto, separate patch?
>
> Also, should the changes for the drivers be in two separate patches also?

That's basically the same driver with different constants so I guess not.

Thanks

Michal

Re: [linux-sunxi] [PATCH 1/5] spi: sunxi: fix transfer timeout

[Julian Calaby]

Hi Michal,

On Fri, May 27, 2016 at 3:05 PM, Michal Suchanek <hramrach@gmail.com> wrote:
> On 27 May 2016 at 04:05, Julian Calaby <julian.calaby@gmail.com> wrote:
>> Hi Michal,
>>
>> On Fri, May 27, 2016 at 5:25 AM, Michal Suchanek <hramrach@gmail.com> wrote:
>>> The trasfer timeout is fixed at 1000 ms. Reading a 4Mbyte flash over
>>> 1MHz SPI bus takes way longer than that. Calculate the timeout from the
>>> actual time the transfer is supposed to take and multiply by 2 for good
>>> measure.
>>>
>>> Signed-off-by: Michal Suchanek <hramrach@gmail.com>
>>> ---
>>>
>>> v2:
>>> - fix build error
>>> - use unsigned instead of int in max_t
>>> - use tfr->speed_hz instead of sspi->max_speed_hz
>>> ---
>>>  drivers/spi/spi-sun4i.c | 11 ++++++++++-
>>>  drivers/spi/spi-sun6i.c | 11 ++++++++++-
>>>  2 files changed, 20 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
>>> index 1ddd9e2..fe63bbd 100644
>>> --- a/drivers/spi/spi-sun4i.c
>>> +++ b/drivers/spi/spi-sun4i.c
>>> @@ -173,6 +173,7 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
>>>  {
>>>         struct sun4i_spi *sspi = spi_master_get_devdata(master);
>>>         unsigned int mclk_rate, div, timeout;
>>> +       unsigned int start, end, tx_time;
>>>         unsigned int tx_len = 0;
>>>         int ret = 0;
>>>         u32 reg;
>>> @@ -279,9 +280,17 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
>>>         reg = sun4i_spi_read(sspi, SUN4I_CTL_REG);
>>>         sun4i_spi_write(sspi, SUN4I_CTL_REG, reg | SUN4I_CTL_XCH);
>>>
>>> +       tx_time = max_t(unsigned, tfr->len * 8 * 2 / (tfr->speed_hz / 1000),
>>
>> You should probably use "unsigned int" instead of just "unsigned" here.
>>
>>> +                       100);
>
> Or just 100U constant and avoid max_t altogether.
>
>>> +       start = jiffies;
>>>         timeout = wait_for_completion_timeout(&sspi->done,
>>> -                                             msecs_to_jiffies(1000));
>>> +                                             msecs_to_jiffies(tx_time));
>>> +       end = jiffies;
>>>         if (!timeout) {
>>> +               dev_warn(&master->dev,
>>> +                        "%s: timeout transferring %u bytes@%iHz for %i(%i)ms",
>>> +                        dev_name(&spi->dev), tfr->len, tfr->speed_hz,
>>> +                        jiffies_to_msecs(end - start), tx_time);
>>
>> Should the debug changes be in a separate patch?
>
> Is this so big of a change that it needs to be split?

Some people get touchy about changes not being mentioned in the commit
log. Technically this is two changes: fixing the timeout and adding
the timeout debugging, however they're related, so maybe just mention
that you've added this debugging in the commit log.

>
>>
>>>                 ret = -ETIMEDOUT;
>>>                 goto out;
>>>         }
>>> diff --git a/drivers/spi/spi-sun6i.c b/drivers/spi/spi-sun6i.c
>>> index 42e2c4b..8be5c5c 100644
>>> --- a/drivers/spi/spi-sun6i.c
>>> +++ b/drivers/spi/spi-sun6i.c
>>> @@ -162,6 +162,7 @@ static int sun6i_spi_transfer_one(struct spi_master *master,
>>>         unsigned int mclk_rate, div, timeout;
>>>         unsigned int tx_len = 0;
>>>         int ret = 0;
>>> +       unsigned int start, end, tx_time;
>>>         u32 reg;
>>>
>>>         /* We don't support transfer larger than the FIFO */
>>> @@ -269,9 +270,17 @@ static int sun6i_spi_transfer_one(struct spi_master *master,
>>>         reg = sun6i_spi_read(sspi, SUN6I_TFR_CTL_REG);
>>>         sun6i_spi_write(sspi, SUN6I_TFR_CTL_REG, reg | SUN6I_TFR_CTL_XCH);
>>>
>>> +       tx_time = max_t(unsigned, tfr->len * 8 * 2 / (tfr->speed_hz / 1000),
>>
>> Ditto, "unsigned int" instead of "unsigned"?
>>
>>> +                       100);
>>> +       start = jiffies;
>>>         timeout = wait_for_completion_timeout(&sspi->done,
>>> -                                             msecs_to_jiffies(1000));
>>> +                                             msecs_to_jiffies(tx_time));
>>> +       end = jiffies;
>>>         if (!timeout) {
>>> +               dev_warn(&master->dev,
>>> +                        "%s: timeout transferring %u bytes@%iHz for %i(%i)ms",
>>> +                        dev_name(&spi->dev), tfr->len, tfr->speed_hz,
>>> +                        jiffies_to_msecs(end - start), tx_time);
>>
>> Ditto, separate patch?
>>
>> Also, should the changes for the drivers be in two separate patches also?
>
> That's basically the same driver with different constants so I guess not.

Fair enough, I withdraw my comment then.

Thanks,

-- 
Julian Calaby

Email: julian.calaby@gmail.com
Profile: http://www.google.com/profiles/julian.calaby/

Re: [PATCH 2/5] spi: sun4i: fix FIFO limit

[Maxime Ripard]

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Hi,

On Thu, May 26, 2016 at 07:25:24PM -0000, Michal Suchanek wrote:
> When testing SPI without DMA I noticed that filling the FIFO on the
> spi controller causes timeout.
> 
> Always leave room for one byte in the FIFO.
> 
> Signed-off-by: Michal Suchanek <hramrach@gmail.com>

Sending it to stable would be great (with a fixes tag too).

> 
> ---
> v2:
> use EMSGSIZE instead of EINVAL
> ---
>  drivers/spi/spi-sun4i.c | 8 ++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
> index fe63bbd..04f1b77 100644
> --- a/drivers/spi/spi-sun4i.c
> +++ b/drivers/spi/spi-sun4i.c
> @@ -180,7 +180,9 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
>  
>  	/* We don't support transfer larger than the FIFO */
>  	if (tfr->len > SUN4I_FIFO_DEPTH)
> -		return -EINVAL;
> +		return -EMSGSIZE;

One new line here.

> +	if (tfr->tx_buf && tfr->len >= SUN4I_FIFO_DEPTH)
> +		return -EMSGSIZE;
>  
>  	reinit_completion(&sspi->done);
>  	sspi->tx_buf = tfr->tx_buf;
> @@ -271,7 +273,9 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
>  	sun4i_spi_write(sspi, SUN4I_XMIT_CNT_REG, SUN4I_XMIT_CNT(tx_len));
>  
>  	/* Fill the TX FIFO */
> -	sun4i_spi_fill_fifo(sspi, SUN4I_FIFO_DEPTH);
> +	/* Filling the FIFO fully causes timeout for some reason
> +	 * at least on spi2 on A10s */

This is not the proper comment style and generate a warning with
checkpatch, please fix that (and merge the comment with the previous
comment).

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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Re: [PATCH 3/5] spi: sunxi: expose maximum transfer size limit

[Maxime Ripard]

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On Thu, May 26, 2016 at 07:25:24PM -0000, Michal Suchanek wrote:
> The sun4i spi hardware can trasfer at most 63 bytes of data without DMA
> support so report the limitation. Same on sun6i.

Is it? Is there timeouts on the A31 and later SoCs?

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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Re: [PATCH 3/5] spi: sunxi: expose maximum transfer size limit

[Michal Suchanek]

Hello,

On 30 May 2016 at 10:37, Maxime Ripard <maxime.ripard@free-electrons.com> wrote:
> On Thu, May 26, 2016 at 07:25:24PM -0000, Michal Suchanek wrote:
>> The sun4i spi hardware can trasfer at most 63 bytes of data without DMA
>> support so report the limitation. Same on sun6i.
>
> Is it? Is there timeouts on the A31 and later SoCs?
>

I have no sun6i hardware to test with.

This is an advisory limit you can query and it better be smaller
rather than unreliable. The hard limit in the driver is still
SUN6I_FIFO_DEPTH (which is 128 bytes on sun6i).

You can test his without any actual SPI device. Unused pins you can
multiplex as SPI suffice.

Thanks

Michal

Re: [PATCH 4/5] spi: sunxi: set maximum and minimum speed of SPI master

[Maxime Ripard]

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Hi,

On Thu, May 26, 2016 at 07:25:25PM -0000, Michal Suchanek wrote:
> The maximum speed of SPI master is used when maximum speed of SPI slave
> is not specified. Also the __spi_validate function should check that
> transfer speeds do not exceed the master limits.
> 
> The user manual for A10 and A31 specifies maximum
> speed of the SPI clock as 100MHz and minimum as 3kHz.
> 
> Setting the SPI clock to out-of-spec values can lock up the SoC.
> 
> Signed-off-by: Michal Suchanek <hramrach@gmail.com>
> ---
>  drivers/spi/spi-sun4i.c | 2 ++
>  drivers/spi/spi-sun6i.c | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
> index bf52b09..e1a75dd6 100644
> --- a/drivers/spi/spi-sun4i.c
> +++ b/drivers/spi/spi-sun4i.c
> @@ -405,6 +405,8 @@ static int sun4i_spi_probe(struct platform_device *pdev)
>  	}
>  
>  	sspi->master = master;
> +	master->max_speed_hz = 100*1000*1000;

You need spaces around the * operator.

> +	master->min_speed_hz =        3*1000;

And I'm not exactly sure why you have that weird indentation.

The same applies for the sun6i driver

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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Re: [PATCH 1/5] spi: sunxi: fix transfer timeout

[Maxime Ripard]

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On Thu, May 26, 2016 at 07:25:23PM -0000, Michal Suchanek wrote:
> The trasfer timeout is fixed at 1000 ms. Reading a 4Mbyte flash over
> 1MHz SPI bus takes way longer than that. Calculate the timeout from the
> actual time the transfer is supposed to take and multiply by 2 for good
> measure.
> 
> Signed-off-by: Michal Suchanek <hramrach@gmail.com>
> ---
> 
> v2:
> - fix build error
> - use unsigned instead of int in max_t

And this generates warnings in checkpatch. Please make sure that you
run it before submitting any patches.

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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Re: [linux-sunxi] [PATCH 1/5] spi: sunxi: fix transfer timeout

[Mark Brown]

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On Fri, May 27, 2016 at 03:10:11PM +1000, Julian Calaby wrote:
> On Fri, May 27, 2016 at 3:05 PM, Michal Suchanek <hramrach@gmail.com> wrote:

> >> Also, should the changes for the drivers be in two separate patches also?

> > That's basically the same driver with different constants so I guess not.

> Fair enough, I withdraw my comment then.

If it's the same driver with different constants it should really
actually be the same driver - I did ask this when the drivers were
originally merged...

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Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

[Mark Brown]

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On Thu, May 26, 2016 at 07:25:25PM -0000, Michal Suchanek wrote:

>  - fallback to previous behaviour when DMA initialization fails
> 
>    + this has the problem that when the driver happens to load before the dma
>      driver it will not use dma - can be addressed with a module parameter

No, you should pay attention to the error you are getting and let probe
deferral happen if that's the error you get.

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Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

[Geert Uytterhoeven]

Hi Mark,

On Mon, May 30, 2016 at 1:26 PM, Mark Brown <broonie@kernel.org> wrote:
> On Thu, May 26, 2016 at 07:25:25PM -0000, Michal Suchanek wrote:
>>  - fallback to previous behaviour when DMA initialization fails
>>
>>    + this has the problem that when the driver happens to load before the dma
>>      driver it will not use dma - can be addressed with a module parameter
>
> No, you should pay attention to the error you are getting and let probe
> deferral happen if that's the error you get.

Unfortunately DMA is an optional feature.

There's no way to distinguish between -EPROBE_DEFER due to the SPI master
driver being probed before the DMA engine driver, and -EPROBE_DEFER due to
support for the DMA engine not having been compiled in.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

[Mark Brown]

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On Mon, May 30, 2016 at 02:11:51PM +0200, Geert Uytterhoeven wrote:
> On Mon, May 30, 2016 at 1:26 PM, Mark Brown <broonie@kernel.org> wrote:
> > On Thu, May 26, 2016 at 07:25:25PM -0000, Michal Suchanek wrote:
> >>  - fallback to previous behaviour when DMA initialization fails
> >>
> >>    + this has the problem that when the driver happens to load before the dma
> >>      driver it will not use dma - can be addressed with a module parameter

> > No, you should pay attention to the error you are getting and let probe
> > deferral happen if that's the error you get.

> Unfortunately DMA is an optional feature.

> There's no way to distinguish between -EPROBE_DEFER due to the SPI master
> driver being probed before the DMA engine driver, and -EPROBE_DEFER due to
> support for the DMA engine not having been compiled in.

I really don't think it's worth caring too much about cases where the
DMA driver hasn't been compiled in, it's not like SPI is the only thing
that's going to be using it.  I really think it's better to defer the
problem - not getting DMA (or worse, only getting DMA on some boots) is
not great and if people are optimising on that level my feeling is that
they're probably going to be OK with customizing DT to match.  Ideally
we would have something a bit nicer than deferred probe but right now
this seems the more helpful option.

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Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

[Michal Suchanek]

Hello,

On 30 May 2016 at 17:03, Mark Brown <broonie@kernel.org> wrote:
> On Mon, May 30, 2016 at 02:11:51PM +0200, Geert Uytterhoeven wrote:
>> On Mon, May 30, 2016 at 1:26 PM, Mark Brown <broonie@kernel.org> wrote:
>> > On Thu, May 26, 2016 at 07:25:25PM -0000, Michal Suchanek wrote:
>> >>  - fallback to previous behaviour when DMA initialization fails
>> >>
>> >>    + this has the problem that when the driver happens to load before the dma
>> >>      driver it will not use dma - can be addressed with a module parameter
>
>> > No, you should pay attention to the error you are getting and let probe
>> > deferral happen if that's the error you get.
>
>> Unfortunately DMA is an optional feature.
>
>> There's no way to distinguish between -EPROBE_DEFER due to the SPI master
>> driver being probed before the DMA engine driver, and -EPROBE_DEFER due to
>> support for the DMA engine not having been compiled in.
>
> I really don't think it's worth caring too much about cases where the
> DMA driver hasn't been compiled in, it's not like SPI is the only thing
> that's going to be using it.  I really think it's better to defer the
> problem - not getting DMA (or worse, only getting DMA on some boots) is
> not great and if people are optimising on that level my feeling is that
> they're probably going to be OK with customizing DT to match.  Ideally
> we would have something a bit nicer than deferred probe but right now
> this seems the more helpful option.

It's what the driver did to start with and it was requested to fall
back to non-DMA in the case DMA is not available.

We get to the much discussed problem that it's never possible to tell
if a driver is available or not.

It's possible to add a parameter like require_dma which could be used
to load the driver without dma if unset. If it was set by default then
driver ordering is not important so long as dma driver is loaded
eventually. Also an informative print that such parameter exists when
probing the driver is deferred would be helpful. It would probably
create quite a bit of log spam, however. The driver can be deferred
several times during boot.

Thanks

Michal

Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

[Mark Brown]

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On Mon, May 30, 2016 at 05:28:10PM +0200, Michal Suchanek wrote:
> On 30 May 2016 at 17:03, Mark Brown <broonie@kernel.org> wrote:

> > I really don't think it's worth caring too much about cases where the
> > DMA driver hasn't been compiled in, it's not like SPI is the only thing

> It's what the driver did to start with and it was requested to fall
> back to non-DMA in the case DMA is not available.

Why?  I really can't see any sensible use case for this that doesn't
have a better solution available.

> It's possible to add a parameter like require_dma which could be used
> to load the driver without dma if unset. If it was set by default then
> driver ordering is not important so long as dma driver is loaded
> eventually. Also an informative print that such parameter exists when
> probing the driver is deferred would be helpful. It would probably
> create quite a bit of log spam, however. The driver can be deferred
> several times during boot.

That seems fairly hacky, if we were going to do anything like that it
should be the other way around so that we default to trying to use
resources and even then it seems like something that should be handled
at a framework level rather than having random options in individual
drivers to ignore things.  Having things behave inconsistently between
different drivers is going to lead to a worse user experience and if
this is a good idea for one driver it seems like it'd be a good idea for
all of them.

But really 

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Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

[Michal Suchanek]

On 30 May 2016 at 17:50, Mark Brown <broonie@kernel.org> wrote:
> On Mon, May 30, 2016 at 05:28:10PM +0200, Michal Suchanek wrote:
>> On 30 May 2016 at 17:03, Mark Brown <broonie@kernel.org> wrote:
>
>> > I really don't think it's worth caring too much about cases where the
>> > DMA driver hasn't been compiled in, it's not like SPI is the only thing
>
>> It's what the driver did to start with and it was requested to fall
>> back to non-DMA in the case DMA is not available.
>
> Why?  I really can't see any sensible use case for this that doesn't
> have a better solution available.

Of course, the solution is to compile in the DMA driver.

It's been argued that some drivers which use only short transfers will
just work.

>
>> It's possible to add a parameter like require_dma which could be used
>> to load the driver without dma if unset. If it was set by default then
>> driver ordering is not important so long as dma driver is loaded
>> eventually. Also an informative print that such parameter exists when
>> probing the driver is deferred would be helpful. It would probably
>> create quite a bit of log spam, however. The driver can be deferred
>> several times during boot.
>
> That seems fairly hacky, if we were going to do anything like that it
> should be the other way around so that we default to trying to use
> resources and even then it seems like something that should be handled
> at a framework level rather than having random options in individual
> drivers to ignore things.  Having things behave inconsistently between
> different drivers is going to lead to a worse user experience and if
> this is a good idea for one driver it seems like it'd be a good idea for
> all of them.

Hacky but doable if desirable. It's awesome for testing SPI transfer
fragmentation with different drivers ;-)

The previous discussion of this driver is here
http://thread.gmane.org/gmane.linux.kernel/2162327

Thanks

Michal

Re: [linux-sunxi] [PATCH 1/5] spi: sunxi: fix transfer timeout

[Michal Suchanek]

Hello

On 30 May 2016 at 13:23, Mark Brown <broonie@kernel.org> wrote:
> On Fri, May 27, 2016 at 03:10:11PM +1000, Julian Calaby wrote:
>> On Fri, May 27, 2016 at 3:05 PM, Michal Suchanek <hramrach@gmail.com> wrote:
>
>> >> Also, should the changes for the drivers be in two separate patches also?
>
>> > That's basically the same driver with different constants so I guess not.
>
>> Fair enough, I withdraw my comment then.
>
> If it's the same driver with different constants it should really
> actually be the same driver - I did ask this when the drivers were
> originally merged...

There are some slight differences and the constants really are
different for each driver.

You would need a register remap adaptation layer and a few qirks for
each revision of the driver.

It's certainly possible to merge them but I am not sure if that gives
easier to maintain code.

On the other hand, comparing the drivers there is different comment
anout clock calculation arithmetic and the code is the same :S

Thanks

Michal

--- spi-sun4i.c    2016-05-31 13:19:27.076510421 +0200
+++ spi-sun6i.c    2016-05-31 13:26:58.123580382 +0200
@@ -19,65 +19,72 @@
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
+#include <linux/reset.h>

 #include <linux/spi/spi.h>

-#define SUNXI_FIFO_DEPTH            64
+#define SUNXI_FIFO_DEPTH            128

-#define SUNXI_RXDATA_REG            0x00
+#define SUNXI_TXDATA_REG            0x200

-#define SUNXI_TXDATA_REG            0x04
+#define SUNXI_RXDATA_REG            0x300

 #define SUNXI_TFR_CTL_REG            0x08
-#define SUNXI_TFR_CTL_ENABLE            BIT(0)
-#define SUNXI_TFR_CTL_MASTER            BIT(1)
-#define SUNXI_TFR_CTL_CPHA            BIT(2)
-#define SUNXI_TFR_CTL_CPOL            BIT(3)
-#define SUNXI_TFR_CTL_CS_ACTIVE_LOW        BIT(4)
-#define SUNXI_TFR_CTL_LMTF            BIT(6)
-#define SUNXI_TFR_CTL_TF_RST            BIT(8)
-#define SUNXI_TFR_CTL_RF_RST            BIT(9)
-#define SUNXI_TFR_CTL_XCH            BIT(10)
-#define SUNXI_TFR_CTL_CS_MASK            0x3000
-#define SUNXI_TFR_CTL_CS(cs)            (((cs) << 12) & SUNXI_TFR_CTL_CS_MASK)
-#define SUNXI_TFR_CTL_DHB            BIT(15)
-#define SUNXI_TFR_CTL_CS_MANUAL            BIT(16)
-#define SUNXI_TFR_CTL_CS_LEVEL            BIT(17)
-#define SUNXI_TFR_CTL_TP            BIT(18)
+#define SUNXI_TFR_CTL_CPHA            BIT(0)
+#define SUNXI_TFR_CTL_CPOL            BIT(1)
+#define SUNXI_TFR_CTL_SPOL            BIT(2)
+#define SUNXI_TFR_CTL_CS_MASK            0x30
+#define SUNXI_TFR_CTL_CS(cs)            (((cs) << 4) & SUNXI_TFR_CTL_CS_MASK)
+#define SUNXI_TFR_CTL_CS_MANUAL            BIT(6)
+#define SUNXI_TFR_CTL_CS_LEVEL            BIT(7)
+#define SUNXI_TFR_CTL_DHB            BIT(8)
+#define SUNXI_TFR_CTL_FBS            BIT(12)
+#define SUNXI_TFR_CTL_XCH            BIT(31)

-#define SUNXI_INT_CTL_REG            0x0c
-#define SUNXI_INT_CTL_TC            BIT(16)
+#define SUNXI_INT_CTL_REG            0x10
+#define SUNXI_INT_CTL_RF_OVF            BIT(8)
+#define SUNXI_INT_CTL_TC            BIT(12)

-#define SUNXI_INT_STA_REG            0x10
+#define SUNXI_INT_STA_REG            0x14

-#define SUNXI_DMA_CTL_REG            0x14
+#define SUNXI_FIFO_CTL_REG            0x18
+#define SUNXI_FIFO_CTL_RF_RST            BIT(15)
+#define SUNXI_FIFO_CTL_TF_RST            BIT(31)

-#define SUNXI_CLK_CTL_REG            0x1c
+#define SUNXI_CLK_CTL_REG            0x24
 #define SUNXI_CLK_CTL_CDR2_MASK            0xff
 #define SUNXI_CLK_CTL_CDR2(div)            (((div) &
SUNXI_CLK_CTL_CDR2_MASK) << 0)
 #define SUNXI_CLK_CTL_CDR1_MASK            0xf
 #define SUNXI_CLK_CTL_CDR1(div)            (((div) &
SUNXI_CLK_CTL_CDR1_MASK) << 8)
 #define SUNXI_CLK_CTL_DRS            BIT(12)

-#define SUNXI_BURST_CNT_REG            0x20
+#define SUNXI_BURST_CNT_REG            0x30
 #define SUNXI_BURST_CNT(cnt)            ((cnt) & 0xffffff)

-#define SUNXI_XMIT_CNT_REG            0x24
+#define SUNXI_XMIT_CNT_REG            0x34
 #define SUNXI_XMIT_CNT(cnt)            ((cnt) & 0xffffff)

-#define SUNXI_FIFO_STA_REG            0x28
+#define SUNXI_FIFO_STA_REG            0x1c
 #define SUNXI_FIFO_STA_RF_CNT_MASK        0x7f
 #define SUNXI_FIFO_STA_RF_CNT_BITS        0
 #define SUNXI_FIFO_STA_TF_CNT_MASK        0x7f
 #define SUNXI_FIFO_STA_TF_CNT_BITS        16

-#define SUNXI_WAIT_REG                0x18
+#define SUNXI_BURST_CTL_CNT_REG            0x38
+#define SUNXI_BURST_CTL_CNT_STC(cnt)        ((cnt) & 0xffffff)
+
+#define SUNXI_GBL_CTL_REG            0x04
+#define SUNXI_GBL_CTL_BUS_ENABLE        BIT(0)
+#define SUNXI_GBL_CTL_MASTER            BIT(1)
+#define SUNXI_GBL_CTL_TP            BIT(7)
+#define SUNXI_GBL_CTL_RST            BIT(31)

 struct sunxi_spi {
     struct spi_master    *master;
     void __iomem        *base_addr;
     struct clk        *hclk;
     struct clk        *mclk;
+    struct reset_control    *rstc;

     struct completion    done;

@@ -136,37 +143,18 @@
     u32 reg;

     reg = sunxi_spi_read(sspi, SUNXI_TFR_CTL_REG);
-
     reg &= ~SUNXI_TFR_CTL_CS_MASK;
     reg |= SUNXI_TFR_CTL_CS(spi->chip_select);

-    /* We want to control the chip select manually */
-    reg |= SUNXI_TFR_CTL_CS_MANUAL;
-
     if (enable)
         reg |= SUNXI_TFR_CTL_CS_LEVEL;
     else
         reg &= ~SUNXI_TFR_CTL_CS_LEVEL;

-    /*
-     * Even though this looks irrelevant since we are supposed to
-     * be controlling the chip select manually, this bit also
-     * controls the levels of the chip select for inactive
-     * devices.
-     *
-     * If we don't set it, the chip select level will go low by
-     * default when the device is idle, which is not really
-     * expected in the common case where the chip select is active
-     * low.
-     */
-    if (spi->mode & SPI_CS_HIGH)
-        reg &= ~SUNXI_TFR_CTL_CS_ACTIVE_LOW;
-    else
-        reg |= SUNXI_TFR_CTL_CS_ACTIVE_LOW;
-
     sunxi_spi_write(sspi, SUNXI_TFR_CTL_REG, reg);
 }

+
 static int sunxi_spi_transfer_one(struct spi_master *master,
                   struct spi_device *spi,
                   struct spi_transfer *tfr)
@@ -189,17 +177,16 @@
     /* Clear pending interrupts */
     sunxi_spi_write(sspi, SUNXI_INT_STA_REG, ~0);

-
-    reg = sunxi_spi_read(sspi, SUNXI_TFR_CTL_REG);
-
     /* Reset FIFOs */
-    sunxi_spi_write(sspi, SUNXI_TFR_CTL_REG,
-            reg | SUNXI_TFR_CTL_RF_RST | SUNXI_TFR_CTL_TF_RST);
+    sunxi_spi_write(sspi, SUNXI_FIFO_CTL_REG,
+            SUNXI_FIFO_CTL_RF_RST | SUNXI_FIFO_CTL_TF_RST);

     /*
      * Setup the transfer control register: Chip Select,
      * polarities, etc.
      */
+    reg = sunxi_spi_read(sspi, SUNXI_TFR_CTL_REG);
+
     if (spi->mode & SPI_CPOL)
         reg |= SUNXI_TFR_CTL_CPOL;
     else
@@ -211,10 +198,9 @@
         reg &= ~SUNXI_TFR_CTL_CPHA;

     if (spi->mode & SPI_LSB_FIRST)
-        reg |= SUNXI_TFR_CTL_LMTF;
+        reg |= SUNXI_TFR_CTL_FBS;
     else
-        reg &= ~SUNXI_TFR_CTL_LMTF;
-
+        reg &= ~SUNXI_TFR_CTL_FBS;

     /*
      * If it's a TX only transfer, we don't want to fill the RX
@@ -225,6 +211,9 @@
     else
         reg |= SUNXI_TFR_CTL_DHB;

+    /* We want to control the chip select manually */
+    reg |= SUNXI_TFR_CTL_CS_MANUAL;
+
     sunxi_spi_write(sspi, SUNXI_TFR_CTL_REG, reg);

     /* Ensure that we have a parent clock fast enough */
@@ -239,7 +228,7 @@
      *
      * We have two choices there. Either we can use the clock
      * divide rate 1, which is calculated thanks to this formula:
-     * SPI_CLK = MOD_CLK / (2 ^ (cdr + 1))
+     * SPI_CLK = MOD_CLK / (2 ^ cdr)
      * Or we can use CDR2, which is calculated with the formula:
      * SPI_CLK = MOD_CLK / (2 * (cdr + 1))
      * Wether we use the former or the latter is set through the
@@ -268,6 +257,8 @@
     /* Setup the counters */
     sunxi_spi_write(sspi, SUNXI_BURST_CNT_REG, SUNXI_BURST_CNT(tfr->len));
     sunxi_spi_write(sspi, SUNXI_XMIT_CNT_REG, SUNXI_XMIT_CNT(tx_len));
+    sunxi_spi_write(sspi, SUNXI_BURST_CTL_CNT_REG,
+            SUNXI_BURST_CTL_CNT_STC(tx_len));

     /* Fill the TX FIFO */
     sunxi_spi_fill_fifo(sspi, SUNXI_FIFO_DEPTH);
@@ -327,11 +318,19 @@
         goto err;
     }

-    sunxi_spi_write(sspi, SUNXI_TFR_CTL_REG,
-            SUNXI_TFR_CTL_ENABLE | SUNXI_TFR_CTL_MASTER | SUNXI_TFR_CTL_TP);
+    ret = reset_control_deassert(sspi->rstc);
+    if (ret) {
+        dev_err(dev, "Couldn't deassert the device from reset\n");
+        goto err2;
+    }
+
+    sunxi_spi_write(sspi, SUNXI_GBL_CTL_REG,
+            SUNXI_GBL_CTL_BUS_ENABLE | SUNXI_GBL_CTL_MASTER |
SUNXI_GBL_CTL_TP);

     return 0;

+err2:
+    clk_disable_unprepare(sspi->mclk);
 err:
     clk_disable_unprepare(sspi->hclk);
 out:
@@ -343,6 +342,7 @@
     struct spi_master *master = dev_get_drvdata(dev);
     struct sunxi_spi *sspi = spi_master_get_devdata(master);

+    reset_control_assert(sspi->rstc);
     clk_disable_unprepare(sspi->mclk);
     clk_disable_unprepare(sspi->hclk);

@@ -411,6 +411,13 @@

     init_completion(&sspi->done);

+    sspi->rstc = devm_reset_control_get(&pdev->dev, NULL);
+    if (IS_ERR(sspi->rstc)) {
+        dev_err(&pdev->dev, "Couldn't get reset controller\n");
+        ret = PTR_ERR(sspi->rstc);
+        goto err_free_master;
+    }
+
     /*
      * This wake-up/shutdown pattern is to be able to have the
      * device woken up, even if runtime_pm is disabled
@@ -449,7 +456,7 @@
 }

 static const struct of_device_id sunxi_spi_match[] = {
-    { .compatible = "allwinner,sun4i-a10-spi", },
+    { .compatible = "allwinner,sun6i-a31-spi", },
     {}
 };
 MODULE_DEVICE_TABLE(of, sunxi_spi_match);
@@ -472,5 +479,5 @@

 MODULE_AUTHOR("Pan Nan <pannan@allwinnertech.com>");
 MODULE_AUTHOR("Maxime Ripard <maxime.ripard@free-electrons.com>");
-MODULE_DESCRIPTION("Allwinner A1X/A20 SPI controller driver");
+MODULE_DESCRIPTION("Allwinner A31 SPI controller driver");
 MODULE_LICENSE("GPL");

Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

[Mark Brown]

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On Tue, May 31, 2016 at 12:44:54PM +0200, Michal Suchanek wrote:
> On 30 May 2016 at 17:50, Mark Brown <broonie@kernel.org> wrote:
> > On Mon, May 30, 2016 at 05:28:10PM +0200, Michal Suchanek wrote:

> >> It's what the driver did to start with and it was requested to fall
> >> back to non-DMA in the case DMA is not available.

> > Why?  I really can't see any sensible use case for this that doesn't
> > have a better solution available.

> Of course, the solution is to compile in the DMA driver.

> It's been argued that some drivers which use only short transfers will
> just work.

With nothing else in the system that needs DMA?  It's making the
performance of the system less reliable for the benefit of a very narrow
use case.

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Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

[Michal Suchanek]

On 31 May 2016 at 15:27, Mark Brown <broonie@kernel.org> wrote:
> On Tue, May 31, 2016 at 12:44:54PM +0200, Michal Suchanek wrote:
>> On 30 May 2016 at 17:50, Mark Brown <broonie@kernel.org> wrote:
>> > On Mon, May 30, 2016 at 05:28:10PM +0200, Michal Suchanek wrote:
>
>> >> It's what the driver did to start with and it was requested to fall
>> >> back to non-DMA in the case DMA is not available.
>
>> > Why?  I really can't see any sensible use case for this that doesn't
>> > have a better solution available.
>
>> Of course, the solution is to compile in the DMA driver.
>
>> It's been argued that some drivers which use only short transfers will
>> just work.
>
> With nothing else in the system that needs DMA?  It's making the
> performance of the system less reliable for the benefit of a very narrow
> use case.

Some of the platform devices have dedicated DMA *controller* built
into the device IP so the DMA engine really is optional on many sunxi
devices. Besides SPI you definitely need the DMA engine for audio. You
probably don't need it for storage and graphics. I don't have any idea
if it's used for USB and Ethernet.

Thanks

Michal

Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

[Maxime Ripard]

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Hi,

On Mon, May 30, 2016 at 04:50:16PM +0100, Mark Brown wrote:
> On Mon, May 30, 2016 at 05:28:10PM +0200, Michal Suchanek wrote:
> > On 30 May 2016 at 17:03, Mark Brown <broonie@kernel.org> wrote:
> 
> > > I really don't think it's worth caring too much about cases where the
> > > DMA driver hasn't been compiled in, it's not like SPI is the only thing
> 
> > It's what the driver did to start with and it was requested to fall
> > back to non-DMA in the case DMA is not available.
> 
> Why?  I really can't see any sensible use case for this that doesn't
> have a better solution available.

SPI works just fine without DMA, which might just be considered an
(optional) optimisation.

We've been using it without DMA for years now, and it was working just
fine, and it will work even better with the other patches in this
serie. There's no reason to add a hard dependency on something that we
don't really need.

Maxime


-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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Re: [PATCH 3/5] spi: sunxi: expose maximum transfer size limit

[Maxime Ripard]

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On Mon, May 30, 2016 at 10:57:10AM +0200, Michal Suchanek wrote:
> Hello,
> 
> On 30 May 2016 at 10:37, Maxime Ripard <maxime.ripard@free-electrons.com> wrote:
> > On Thu, May 26, 2016 at 07:25:24PM -0000, Michal Suchanek wrote:
> >> The sun4i spi hardware can trasfer at most 63 bytes of data without DMA
> >> support so report the limitation. Same on sun6i.
> >
> > Is it? Is there timeouts on the A31 and later SoCs?
> >
> 
> I have no sun6i hardware to test with.
> 
> This is an advisory limit you can query and it better be smaller
> rather than unreliable. The hard limit in the driver is still
> SUN6I_FIFO_DEPTH (which is 128 bytes on sun6i).
> 
> You can test his without any actual SPI device. Unused pins you can
> multiplex as SPI suffice.

Ok, for the time being:

Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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Re: [linux-sunxi] [PATCH 1/5] spi: sunxi: fix transfer timeout

[Maxime Ripard]

[-- Attachment #1: Type: text/plain, Size: 1638 bytes --]

Hi Mark,

On Mon, May 30, 2016 at 12:23:50PM +0100, Mark Brown wrote:
> On Fri, May 27, 2016 at 03:10:11PM +1000, Julian Calaby wrote:
> > On Fri, May 27, 2016 at 3:05 PM, Michal Suchanek <hramrach@gmail.com> wrote:
> 
> > >> Also, should the changes for the drivers be in two separate patches also?
> 
> > > That's basically the same driver with different constants so I guess not.
> 
> > Fair enough, I withdraw my comment then.
> 
> If it's the same driver with different constants it should really
> actually be the same driver - I did ask this when the drivers were
> originally merged...

I think we already had this discussion a few times :)

The thing is that the SPI framework now deals pretty well with the SPI
controllers, and you basically only have the probe function and how to
start a transfer. Which is nice.

However, the sun4i and sun6i SPI controllers have very significant
register layout differences: the registers offset are different, some
registers in the sun4i have been split in several in the sun6i. So
while I concur that they look alike, merging the two in a single
driver would complicate a lot the code, while we would not be able to
share most of the code, so I am really not sure it's worth it.

Where the issue really lies is that they've been both written at the
same time, and share the same flaws, especially in their probe
method. But that's not really related to the controller itself, but
more because the code has been close to copy/pasted.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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Re: [linux-sunxi] Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

[Priit Laes]

On Wed, 2016-06-01 at 20:00 +0200, Maxime Ripard wrote:
> Hi,
> 
> On Mon, May 30, 2016 at 04:50:16PM +0100, Mark Brown wrote:
> > 
> > On Mon, May 30, 2016 at 05:28:10PM +0200, Michal Suchanek wrote:
> > > 
> > > On 30 May 2016 at 17:03, Mark Brown <broonie@kernel.org> wrote:
> > > 
> > > > 
> > > > I really don't think it's worth caring too much about cases
> > > > where the
> > > > DMA driver hasn't been compiled in, it's not like SPI is the
> > > > only thing
> > > 
> > > It's what the driver did to start with and it was requested to
> > > fall
> > > back to non-DMA in the case DMA is not available.
> > Why?  I really can't see any sensible use case for this that
> > doesn't
> > have a better solution available.
> SPI works just fine without DMA, which might just be considered an
> (optional) optimisation.
> 
> We've been using it without DMA for years now, and it was working
> just
> fine, and it will work even better with the other patches in this
> serie. There's no reason to add a hard dependency on something that
> we
> don't really need.
> 

Actually it non-DMA case works fine if you don't need SPI transfers
larger than SUN4I_FIFO_DEPTH - 1, which is 63 bytes.

This was addressed by this patch, but was never applied:
http://permalink.gmane.org/gmane.linux.kernel.spi.devel/18950

Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

[Maxime Ripard]

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On Tue, May 31, 2016 at 04:19:28PM +0200, Michal Suchanek wrote:
> On 31 May 2016 at 15:27, Mark Brown <broonie@kernel.org> wrote:
> > On Tue, May 31, 2016 at 12:44:54PM +0200, Michal Suchanek wrote:
> >> On 30 May 2016 at 17:50, Mark Brown <broonie@kernel.org> wrote:
> >> > On Mon, May 30, 2016 at 05:28:10PM +0200, Michal Suchanek wrote:
> >
> >> >> It's what the driver did to start with and it was requested to fall
> >> >> back to non-DMA in the case DMA is not available.
> >
> >> > Why?  I really can't see any sensible use case for this that doesn't
> >> > have a better solution available.
> >
> >> Of course, the solution is to compile in the DMA driver.
> >
> >> It's been argued that some drivers which use only short transfers will
> >> just work.
> >
> > With nothing else in the system that needs DMA?  It's making the
> > performance of the system less reliable for the benefit of a very narrow
> > use case.
> 
> Some of the platform devices have dedicated DMA *controller* built
> into the device IP so the DMA engine really is optional on many sunxi
> devices. Besides SPI you definitely need the DMA engine for audio. You
> probably don't need it for storage and graphics. I don't have any idea
> if it's used for USB and Ethernet.

USB and Ethernet have their own dedicated DMA engines. So currently,
the only driver that requires it is the audio codec.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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Re: [linux-sunxi] Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

[Mark Brown]

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On Thu, Jun 02, 2016 at 07:42:26AM +0300, Priit Laes wrote:

> This was addressed by this patch, but was never applied:
> http://permalink.gmane.org/gmane.linux.kernel.spi.devel/18950

I've never seen that patch before, if it was CCed to me there's a good
chance it'd have been deleted unread because you put ARM: at the start
of the subject line which says it's a patch for arch/arm.  You'll need
to resubmit.

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Re: [linux-sunxi] Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

[Michal Suchanek]

On 2 June 2016 at 06:42, Priit Laes <plaes@plaes.org> wrote:
> On Wed, 2016-06-01 at 20:00 +0200, Maxime Ripard wrote:
>> Hi,
>>
>> On Mon, May 30, 2016 at 04:50:16PM +0100, Mark Brown wrote:
>> >
>> > On Mon, May 30, 2016 at 05:28:10PM +0200, Michal Suchanek wrote:
>> > >
>> > > On 30 May 2016 at 17:03, Mark Brown <broonie@kernel.org> wrote:
>> > >
>> > > >
>> > > > I really don't think it's worth caring too much about cases
>> > > > where the
>> > > > DMA driver hasn't been compiled in, it's not like SPI is the
>> > > > only thing
>> > >
>> > > It's what the driver did to start with and it was requested to
>> > > fall
>> > > back to non-DMA in the case DMA is not available.
>> > Why?  I really can't see any sensible use case for this that
>> > doesn't
>> > have a better solution available.
>> SPI works just fine without DMA, which might just be considered an
>> (optional) optimisation.
>>
>> We've been using it without DMA for years now, and it was working
>> just
>> fine, and it will work even better with the other patches in this
>> serie. There's no reason to add a hard dependency on something that
>> we
>> don't really need.
>>
>
> Actually it non-DMA case works fine if you don't need SPI transfers
> larger than SUN4I_FIFO_DEPTH - 1, which is 63 bytes.
>
> This was addressed by this patch, but was never applied:
> http://permalink.gmane.org/gmane.linux.kernel.spi.devel/18950

And the code added in that patch will never run unless you

1) use long spi transfers
2) compile in/load SPI without DMA support

There is no reason for doing 2) since we have do DMA support for sunxi.

So that's another code path that needs maintenance and testing and
likely will not get it.

Thanks

Michal

Re: [linux-sunxi] Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

[Mark Brown]

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On Thu, Jun 02, 2016 at 02:14:26PM +0200, Michal Suchanek wrote:
> On 2 June 2016 at 06:42, Priit Laes <plaes@plaes.org> wrote:
> > On Wed, 2016-06-01 at 20:00 +0200, Maxime Ripard wrote:

> > Actually it non-DMA case works fine if you don't need SPI transfers
> > larger than SUN4I_FIFO_DEPTH - 1, which is 63 bytes.

> > This was addressed by this patch, but was never applied:
> > http://permalink.gmane.org/gmane.linux.kernel.spi.devel/18950

> And the code added in that patch will never run unless you

> 1) use long spi transfers
> 2) compile in/load SPI without DMA support

> There is no reason for doing 2) since we have do DMA support for sunxi.

Well, presumably such code exists and is being worked on?

> So that's another code path that needs maintenance and testing and
> likely will not get it.

Oh, come on.  You might not want to use it yourself but the chances are
that someone will want to use it just like the situation with all the
other SPI drivers.  It's a perfectly reasonable and sensible feature to
support upstream.

I really do not understand why there is such a strong desire to have
these devices be a special snowflake here, the worst that's likely to
happen here is that you're going to end up having to either remove the
DMA controller from the DT or load the driver for it neither of which
seem like the end of the world.

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Re: [linux-sunxi] Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

[Michal Suchanek]

On 2 June 2016 at 16:26, Mark Brown <broonie@kernel.org> wrote:
> On Thu, Jun 02, 2016 at 02:14:26PM +0200, Michal Suchanek wrote:
>> On 2 June 2016 at 06:42, Priit Laes <plaes@plaes.org> wrote:
>> > On Wed, 2016-06-01 at 20:00 +0200, Maxime Ripard wrote:
>
>> > Actually it non-DMA case works fine if you don't need SPI transfers
>> > larger than SUN4I_FIFO_DEPTH - 1, which is 63 bytes.
>
>> > This was addressed by this patch, but was never applied:
>> > http://permalink.gmane.org/gmane.linux.kernel.spi.devel/18950
>
>> And the code added in that patch will never run unless you
>
>> 1) use long spi transfers
>> 2) compile in/load SPI without DMA support
>
>> There is no reason for doing 2) since we have do DMA support for sunxi.
>
> Well, presumably such code exists and is being worked on?

Which code are you referring to?

This is a reply to patch which adds DMA support to the SPI driver so
that it can work for arbitrarily long transfers.

So there is code for fully working driver.

>
>> So that's another code path that needs maintenance and testing and
>> likely will not get it.
>
> Oh, come on.  You might not want to use it yourself but the chances are
> that someone will want to use it just like the situation with all the
> other SPI drivers.  It's a perfectly reasonable and sensible feature to
> support upstream.

Is it?

Once we have *one* driver that works for arbitrarily long transfers
and it works out of the box with the board defconfig 99% of people who
will use the SPI driver for anything will use this driver. Any other
variant will go untested.

And for the driver to also work without DMA you have to *tell* it to
probe without DMA because it cannot know you are not going to load a
DMA driver later.

>
> I really do not understand why there is such a strong desire to have
> these devices be a special snowflake here, the worst that's likely to
> happen here is that you're going to end up having to either remove the
> DMA controller from the DT or load the driver for it neither of which
> seem like the end of the world.

Why would you do that?

Thanks

Michal

Re: [linux-sunxi] Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

[Mark Brown]

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On Sun, Jun 05, 2016 at 01:27:11PM +0200, Michal Suchanek wrote:
> On 2 June 2016 at 16:26, Mark Brown <broonie@kernel.org> wrote:
> > On Thu, Jun 02, 2016 at 02:14:26PM +0200, Michal Suchanek wrote:

> >> And the code added in that patch will never run unless you

> >> 1) use long spi transfers
> >> 2) compile in/load SPI without DMA support

> >> There is no reason for doing 2) since we have do DMA support for sunxi.

> > Well, presumably such code exists and is being worked on?

> Which code are you referring to?

> This is a reply to patch which adds DMA support to the SPI driver so
> that it can work for arbitrarily long transfers.

It sounded like there might be a missing DMA driver?  Though I think I
was misreading the above.

> > Oh, come on.  You might not want to use it yourself but the chances are
> > that someone will want to use it just like the situation with all the
> > other SPI drivers.  It's a perfectly reasonable and sensible feature to
> > support upstream.

> Is it?

> Once we have *one* driver that works for arbitrarily long transfers
> and it works out of the box with the board defconfig 99% of people who
> will use the SPI driver for anything will use this driver. Any other
> variant will go untested.

We don't want multiple drivers for this and general maintainability
reasons, I'm not sure where the idea that we might want multiple drivers
came from?

> And for the driver to also work without DMA you have to *tell* it to
> probe without DMA because it cannot know you are not going to load a
> DMA driver later.

Yes.  This puts the cost on the special snowflake systems that
absolutely cannot have any DMA support in their systems for some reason
while keeping the driver featureful by default, and keeps that cost
fairly small.

> > I really do not understand why there is such a strong desire to have
> > these devices be a special snowflake here, the worst that's likely to
> > happen here is that you're going to end up having to either remove the
> > DMA controller from the DT or load the driver for it neither of which
> > seem like the end of the world.

> Why would you do that?

Like I say I really don't understand why this is.  I'm just saying there
are ways to do this fairly simply if people really want it on their
systems.

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