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Re: [PATCH v5 08/10] spi: expose master transfer size limitation.

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  Re: [PATCH v5 08/10] spi: expose master transfer size limitation. Mark Brown <broonie@kernel.org> - 2015-12-02 00:20 +0100
    Re: [PATCH v5 08/10] spi: expose master transfer size limitation. Michal Suchanek <hramrach@gmail.com> - 2015-12-02 10:40 +0100
    Re: [PATCH v5 08/10] spi: expose master transfer size limitation. Martin Sperl <martin@sperl.org> - 2015-12-04 15:40 +0100
      Re: [PATCH v5 08/10] spi: expose master transfer size limitation. Michal Suchanek <hramrach@gmail.com> - 2015-12-04 17:50 +0100
      Re: [PATCH v5 08/10] spi: expose master transfer size limitation. Mark Brown <broonie@kernel.org> - 2015-12-07 21:20 +0100

#1281305 — Re: [PATCH v5 08/10] spi: expose master transfer size limitation.

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On Tue, Dec 01, 2015 at 04:51:06PM -0000, Michal Suchanek wrote:

> +static inline size_t
> +spi_max_transfer_size(struct spi_device *spi)
> +{
> +	struct spi_master *master = spi->master;
> +	if (!master->max_transfer_size)
> +		return 0;
> +	return master->max_transfer_size(spi);
> +}

Can we change this to return SIZE_MAX instead (ie, the maximum value for
a size_t)?  That way callers don't need to worry if there is a limit, if
they want to handle it they can just unconditionally assume that a limit
will be provided.

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#1281551

On 2 December 2015 at 00:12, Mark Brown <broonie@kernel.org> wrote:
> On Tue, Dec 01, 2015 at 04:51:06PM -0000, Michal Suchanek wrote:
>
>> +static inline size_t
>> +spi_max_transfer_size(struct spi_device *spi)
>> +{
>> +     struct spi_master *master = spi->master;
>> +     if (!master->max_transfer_size)
>> +             return 0;
>> +     return master->max_transfer_size(spi);
>> +}
>
> Can we change this to return SIZE_MAX instead (ie, the maximum value for
> a size_t)?  That way callers don't need to worry if there is a limit, if
> they want to handle it they can just unconditionally assume that a limit
> will be provided.

Yes, that sounds reasonable.

Thanks

Michal
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#1283873

> On 02.12.2015, at 00:12, Mark Brown <broonie@kernel.org> wrote:
> 
> On Tue, Dec 01, 2015 at 04:51:06PM -0000, Michal Suchanek wrote:
> 
>> +static inline size_t
>> +spi_max_transfer_size(struct spi_device *spi)
>> +{
>> +	struct spi_master *master = spi->master;
>> +	if (!master->max_transfer_size)
>> +		return 0;
>> +	return master->max_transfer_size(spi);
>> +}
> 
> Can we change this to return SIZE_MAX instead (ie, the maximum value for
> a size_t)?  That way callers don't need to worry if there is a limit, if
> they want to handle it they can just unconditionally assume that a limit
> will be provided.

As I just came across: spi_master.max_dma_len, so I wonder how this 
value would differ from the proposed spi_master.max_transfer_size
on specific HW?

For all practical purposes I would assume both are identical.

Martin

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#1284010

On 4 December 2015 at 15:30, Martin Sperl <martin@sperl.org> wrote:
>
>> On 02.12.2015, at 00:12, Mark Brown <broonie@kernel.org> wrote:
>>
>> On Tue, Dec 01, 2015 at 04:51:06PM -0000, Michal Suchanek wrote:
>>
>>> +static inline size_t
>>> +spi_max_transfer_size(struct spi_device *spi)
>>> +{
>>> +    struct spi_master *master = spi->master;
>>> +    if (!master->max_transfer_size)
>>> +            return 0;
>>> +    return master->max_transfer_size(spi);
>>> +}
>>
>> Can we change this to return SIZE_MAX instead (ie, the maximum value for
>> a size_t)?  That way callers don't need to worry if there is a limit, if
>> they want to handle it they can just unconditionally assume that a limit
>> will be provided.
>
> As I just came across: spi_master.max_dma_len, so I wonder how this
> value would differ from the proposed spi_master.max_transfer_size
> on specific HW?
>
> For all practical purposes I would assume both are identical.

They aren't.

Some SPI masters don't use DMA. Some SPI master drivers can drive CS
manually so they can glue multiple DMA (or whatever) transfers into
single logical SPI transfer transparently. And some cannot. Hence this
limit.

That said I don't know what is the purpose of spi_master.max_dma_len.
It is seldom used. It seems to be used as a hint for the DMA buffer
size in spi.c only.

It is set in 3 drivers.

Thanks

Michal
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#1285894

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On Fri, Dec 04, 2015 at 03:30:50PM +0100, Martin Sperl wrote:
> > On 02.12.2015, at 00:12, Mark Brown <broonie@kernel.org> wrote:

> > Can we change this to return SIZE_MAX instead (ie, the maximum value for
> > a size_t)?  That way callers don't need to worry if there is a limit, if
> > they want to handle it they can just unconditionally assume that a limit
> > will be provided.

> As I just came across: spi_master.max_dma_len, so I wonder how this 
> value would differ from the proposed spi_master.max_transfer_size
> on specific HW?

> For all practical purposes I would assume both are identical.

Yeah, we should probably just remove the DMA specific one in time though
it may be useful for some devices with built in DMA engines if they're
oddly limited I'm not sure how practical their DMA would be if it
differed from the overall transfer length.

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