RE: [PATCH v3] iio: buffer: align the size of scan bytes to size of the largest element

RE: [PATCH v3] iio: buffer: align the size of scan bytes to size of the largest element

[Lars Möllendorf]

-----Ursprüngliche Nachricht-----
> Von: Lars Möllendorf <lars.moellendorf@plating.de>
> Gesendet: Freitag 13 Dezember 2019 14:58
> An: Jonathan Cameron <jic23@kernel.org>; Hartmut Knaack <knaack.h@gmx.de>; Lars-Peter Clausen <lars@metafoo.de>; Peter Meerwald-Stadler <pmeerw@pmeerw.net>; linux-iio@vger.kernel.org
> CC: Lars Möllendorf <lars.moellendorf@plating.de>
> Betreff: [PATCH v3] iio: buffer: align the size of scan bytes to size of the largest element
> 
> Previous versions of `iio_compute_scan_bytes` only aligned each element
> to its own length (i.e. its own natural alignment). Because multiple
> consecutive sets of scan elements are buffered this does not work in
> case the computed scan bytes do not align with the natural alignment of
> the first scan element in the set.
> 
> This commit fixes this by aligning the scan bytes to the natural
> alignment of the largest scan element in the set.



After re-reading my commit message, I come to the conclusion that it really is sufficient to align the scan bytes to the natural alignment of the *first* element. This would save us the `max()` comparisons for each bit. At the moment I am not at my workstation, but I could submit a v4 next Friday.



> Fixes: 959d2952d124 ("staging:iio: make iio_sw_buffer_preenable much more
> general.")
> Signed-off-by: Lars Möllendorf <lars.moellendorf@plating.de>
> ---
> v3:
>   - Fix the problem description in the commit message
>   - Add "Fixes" tag
> 
> v2:
>   - Fix subject of patch which marked it the first in a set of three.
>   - Add a description of the problem in the commit message
> 
> ---
>  drivers/iio/industrialio-buffer.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> index 5d05c38c4ba9..2f037cd59d53 100644
> --- a/drivers/iio/industrialio-buffer.c
> +++ b/drivers/iio/industrialio-buffer.c
> @@ -546,7 +546,7 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
>  				const unsigned long *mask, bool timestamp)
>  {
>  	unsigned bytes = 0;
> -	int length, i;
> +	int length, i, largest = 0;
> 
>  	/* How much space will the demuxed element take? */
>  	for_each_set_bit(i, mask,
> @@ -554,13 +554,17 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
>  		length = iio_storage_bytes_for_si(indio_dev, i);
>  		bytes = ALIGN(bytes, length);
>  		bytes += length;
> +		largest = max(largest, length);
>  	}
> 
>  	if (timestamp) {
>  		length = iio_storage_bytes_for_timestamp(indio_dev);
>  		bytes = ALIGN(bytes, length);
>  		bytes += length;
> +		largest = max(largest, length);
>  	}
> +
> +	bytes = ALIGN(bytes, largest);
>  	return bytes;
>  }
> 
> --
> 2.23.0
> 

Re: [PATCH v3] iio: buffer: align the size of scan bytes to size of the largest element

[Lars-Peter Clausen]

On 12/15/19 10:09 PM, Lars Möllendorf wrote:
> -----Ursprüngliche Nachricht-----
>> Von: Lars Möllendorf <lars.moellendorf@plating.de>
>> Gesendet: Freitag 13 Dezember 2019 14:58
>> An: Jonathan Cameron <jic23@kernel.org>; Hartmut Knaack <knaack.h@gmx.de>; Lars-Peter Clausen <lars@metafoo.de>; Peter Meerwald-Stadler <pmeerw@pmeerw.net>; linux-iio@vger.kernel.org
>> CC: Lars Möllendorf <lars.moellendorf@plating.de>
>> Betreff: [PATCH v3] iio: buffer: align the size of scan bytes to size of the largest element
>>
>> Previous versions of `iio_compute_scan_bytes` only aligned each element
>> to its own length (i.e. its own natural alignment). Because multiple
>> consecutive sets of scan elements are buffered this does not work in
>> case the computed scan bytes do not align with the natural alignment of
>> the first scan element in the set.
>>
>> This commit fixes this by aligning the scan bytes to the natural
>> alignment of the largest scan element in the set.
> 
> 
> 
> After re-reading my commit message, I come to the conclusion that it really is sufficient to align the scan bytes to the natural alignment of the *first* element. This would save us the `max()` comparisons for each bit. At the moment I am not at my workstation, but I could submit a v4 next Friday.
> 

I thought so too in the beginning, but as Jonathan pointed out, it does
not work for all cases. Lets say you have u16,u16,u32,u16. If all
channels are enabled the size is aligned to the first element, but the
u32 would not be aligned in the second dataset.

> 
> 
>> Fixes: 959d2952d124 ("staging:iio: make iio_sw_buffer_preenable much more
>> general.")
>> Signed-off-by: Lars Möllendorf <lars.moellendorf@plating.de>
>> ---
>> v3:
>>   - Fix the problem description in the commit message
>>   - Add "Fixes" tag
>>
>> v2:
>>   - Fix subject of patch which marked it the first in a set of three.
>>   - Add a description of the problem in the commit message
>>
>> ---
>>  drivers/iio/industrialio-buffer.c | 6 +++++-
>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
>> index 5d05c38c4ba9..2f037cd59d53 100644
>> --- a/drivers/iio/industrialio-buffer.c
>> +++ b/drivers/iio/industrialio-buffer.c
>> @@ -546,7 +546,7 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
>>  				const unsigned long *mask, bool timestamp)
>>  {
>>  	unsigned bytes = 0;
>> -	int length, i;
>> +	int length, i, largest = 0;
>>
>>  	/* How much space will the demuxed element take? */
>>  	for_each_set_bit(i, mask,
>> @@ -554,13 +554,17 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
>>  		length = iio_storage_bytes_for_si(indio_dev, i);
>>  		bytes = ALIGN(bytes, length);
>>  		bytes += length;
>> +		largest = max(largest, length);
>>  	}
>>
>>  	if (timestamp) {
>>  		length = iio_storage_bytes_for_timestamp(indio_dev);
>>  		bytes = ALIGN(bytes, length);
>>  		bytes += length;
>> +		largest = max(largest, length);
>>  	}
>> +
>> +	bytes = ALIGN(bytes, largest);
>>  	return bytes;
>>  }
>>
>> --
>> 2.23.0
>>

Re: [PATCH v3] iio: buffer: align the size of scan bytes to size of the largest element

[Jonathan Cameron]

On Mon, 16 Dec 2019 08:51:27 +0100
Lars-Peter Clausen <lars@metafoo.de> wrote:

> On 12/15/19 10:09 PM, Lars Möllendorf wrote:
> > -----Ursprüngliche Nachricht-----  
> >> Von: Lars Möllendorf <lars.moellendorf@plating.de>
> >> Gesendet: Freitag 13 Dezember 2019 14:58
> >> An: Jonathan Cameron <jic23@kernel.org>; Hartmut Knaack <knaack.h@gmx.de>; Lars-Peter Clausen <lars@metafoo.de>; Peter Meerwald-Stadler <pmeerw@pmeerw.net>; linux-iio@vger.kernel.org
> >> CC: Lars Möllendorf <lars.moellendorf@plating.de>
> >> Betreff: [PATCH v3] iio: buffer: align the size of scan bytes to size of the largest element
> >>
> >> Previous versions of `iio_compute_scan_bytes` only aligned each element
> >> to its own length (i.e. its own natural alignment). Because multiple
> >> consecutive sets of scan elements are buffered this does not work in
> >> case the computed scan bytes do not align with the natural alignment of
> >> the first scan element in the set.
> >>
> >> This commit fixes this by aligning the scan bytes to the natural
> >> alignment of the largest scan element in the set.  
> > 
> > 
> > 
> > After re-reading my commit message, I come to the conclusion that it really is sufficient to align the scan bytes to the natural alignment of the *first* element. This would save us the `max()` comparisons for each bit. At the moment I am not at my workstation, but I could submit a v4 next Friday.
> >   
> 
> I thought so too in the beginning, but as Jonathan pointed out, it does
> not work for all cases. Lets say you have u16,u16,u32,u16. If all
> channels are enabled the size is aligned to the first element, but the
> u32 would not be aligned in the second dataset.
> 

I'm sitting on this at the moment... Can I confirm we have consensus
that this patch is the correct fix?

Lars and Lars?

Thanks,

Jonathan


> > 
> >   
> >> Fixes: 959d2952d124 ("staging:iio: make iio_sw_buffer_preenable much more
> >> general.")
> >> Signed-off-by: Lars Möllendorf <lars.moellendorf@plating.de>
> >> ---
> >> v3:
> >>   - Fix the problem description in the commit message
> >>   - Add "Fixes" tag
> >>
> >> v2:
> >>   - Fix subject of patch which marked it the first in a set of three.
> >>   - Add a description of the problem in the commit message
> >>
> >> ---
> >>  drivers/iio/industrialio-buffer.c | 6 +++++-
> >>  1 file changed, 5 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> >> index 5d05c38c4ba9..2f037cd59d53 100644
> >> --- a/drivers/iio/industrialio-buffer.c
> >> +++ b/drivers/iio/industrialio-buffer.c
> >> @@ -546,7 +546,7 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
> >>  				const unsigned long *mask, bool timestamp)
> >>  {
> >>  	unsigned bytes = 0;
> >> -	int length, i;
> >> +	int length, i, largest = 0;
> >>
> >>  	/* How much space will the demuxed element take? */
> >>  	for_each_set_bit(i, mask,
> >> @@ -554,13 +554,17 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
> >>  		length = iio_storage_bytes_for_si(indio_dev, i);
> >>  		bytes = ALIGN(bytes, length);
> >>  		bytes += length;
> >> +		largest = max(largest, length);
> >>  	}
> >>
> >>  	if (timestamp) {
> >>  		length = iio_storage_bytes_for_timestamp(indio_dev);
> >>  		bytes = ALIGN(bytes, length);
> >>  		bytes += length;
> >> +		largest = max(largest, length);
> >>  	}
> >> +
> >> +	bytes = ALIGN(bytes, largest);
> >>  	return bytes;
> >>  }
> >>
> >> --
> >> 2.23.0
> >>  
> 

Re: [PATCH v3] iio: buffer: align the size of scan bytes to size of the largest element

[Lars-Peter Clausen]

On 12/23/19 6:05 PM, Jonathan Cameron wrote:
> On Mon, 16 Dec 2019 08:51:27 +0100
> Lars-Peter Clausen <lars@metafoo.de> wrote:
> 
>> On 12/15/19 10:09 PM, Lars Möllendorf wrote:
>>> -----Ursprüngliche Nachricht-----  
>>>> Von: Lars Möllendorf <lars.moellendorf@plating.de>
>>>> Gesendet: Freitag 13 Dezember 2019 14:58
>>>> An: Jonathan Cameron <jic23@kernel.org>; Hartmut Knaack <knaack.h@gmx.de>; Lars-Peter Clausen <lars@metafoo.de>; Peter Meerwald-Stadler <pmeerw@pmeerw.net>; linux-iio@vger.kernel.org
>>>> CC: Lars Möllendorf <lars.moellendorf@plating.de>
>>>> Betreff: [PATCH v3] iio: buffer: align the size of scan bytes to size of the largest element
>>>>
>>>> Previous versions of `iio_compute_scan_bytes` only aligned each element
>>>> to its own length (i.e. its own natural alignment). Because multiple
>>>> consecutive sets of scan elements are buffered this does not work in
>>>> case the computed scan bytes do not align with the natural alignment of
>>>> the first scan element in the set.
>>>>
>>>> This commit fixes this by aligning the scan bytes to the natural
>>>> alignment of the largest scan element in the set.  
>>>
>>>
>>>
>>> After re-reading my commit message, I come to the conclusion that it really is sufficient to align the scan bytes to the natural alignment of the *first* element. This would save us the `max()` comparisons for each bit. At the moment I am not at my workstation, but I could submit a v4 next Friday.
>>>   
>>
>> I thought so too in the beginning, but as Jonathan pointed out, it does
>> not work for all cases. Lets say you have u16,u16,u32,u16. If all
>> channels are enabled the size is aligned to the first element, but the
>> u32 would not be aligned in the second dataset.
>>
> 
> I'm sitting on this at the moment... Can I confirm we have consensus
> that this patch is the correct fix?
> 
> Lars and Lars?

Current version looks good to me.

Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>

> 
> Thanks,
> 
> Jonathan
> 
> 
>>>
>>>   
>>>> Fixes: 959d2952d124 ("staging:iio: make iio_sw_buffer_preenable much more
>>>> general.")
>>>> Signed-off-by: Lars Möllendorf <lars.moellendorf@plating.de>
>>>> ---
>>>> v3:
>>>>   - Fix the problem description in the commit message
>>>>   - Add "Fixes" tag
>>>>
>>>> v2:
>>>>   - Fix subject of patch which marked it the first in a set of three.
>>>>   - Add a description of the problem in the commit message
>>>>
>>>> ---
>>>>  drivers/iio/industrialio-buffer.c | 6 +++++-
>>>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
>>>> index 5d05c38c4ba9..2f037cd59d53 100644
>>>> --- a/drivers/iio/industrialio-buffer.c
>>>> +++ b/drivers/iio/industrialio-buffer.c
>>>> @@ -546,7 +546,7 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
>>>>  				const unsigned long *mask, bool timestamp)
>>>>  {
>>>>  	unsigned bytes = 0;
>>>> -	int length, i;
>>>> +	int length, i, largest = 0;
>>>>
>>>>  	/* How much space will the demuxed element take? */
>>>>  	for_each_set_bit(i, mask,
>>>> @@ -554,13 +554,17 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
>>>>  		length = iio_storage_bytes_for_si(indio_dev, i);
>>>>  		bytes = ALIGN(bytes, length);
>>>>  		bytes += length;
>>>> +		largest = max(largest, length);
>>>>  	}
>>>>
>>>>  	if (timestamp) {
>>>>  		length = iio_storage_bytes_for_timestamp(indio_dev);
>>>>  		bytes = ALIGN(bytes, length);
>>>>  		bytes += length;
>>>> +		largest = max(largest, length);
>>>>  	}
>>>> +
>>>> +	bytes = ALIGN(bytes, largest);
>>>>  	return bytes;
>>>>  }
>>>>
>>>> --
>>>> 2.23.0
>>>>  
>>
> 

Re: [PATCH v3] iio: buffer: align the size of scan bytes to size of the largest element

[Lars Möllendorf]

[-- Attachment #1: Type: text/plain, Size: 6106 bytes --]



On 26.12.19 22:16, Lars-Peter Clausen wrote:
> On 12/23/19 6:05 PM, Jonathan Cameron wrote:
>> On Mon, 16 Dec 2019 08:51:27 +0100
>> Lars-Peter Clausen <lars@metafoo.de> wrote:
>>
>>> On 12/15/19 10:09 PM, Lars Möllendorf wrote:
>>>> -----Ursprüngliche Nachricht-----  
>>>>> Von: Lars Möllendorf <lars.moellendorf@plating.de>
>>>>> Gesendet: Freitag 13 Dezember 2019 14:58
>>>>> An: Jonathan Cameron <jic23@kernel.org>; Hartmut Knaack <knaack.h@gmx.de>; Lars-Peter Clausen <lars@metafoo.de>; Peter Meerwald-Stadler <pmeerw@pmeerw.net>; linux-iio@vger.kernel.org
>>>>> CC: Lars Möllendorf <lars.moellendorf@plating.de>
>>>>> Betreff: [PATCH v3] iio: buffer: align the size of scan bytes to size of the largest element
>>>>>
>>>>> Previous versions of `iio_compute_scan_bytes` only aligned each element
>>>>> to its own length (i.e. its own natural alignment). Because multiple
>>>>> consecutive sets of scan elements are buffered this does not work in
>>>>> case the computed scan bytes do not align with the natural alignment of
>>>>> the first scan element in the set.
>>>>>
>>>>> This commit fixes this by aligning the scan bytes to the natural
>>>>> alignment of the largest scan element in the set.  
>>>>
>>>>
>>>>
>>>> After re-reading my commit message, I come to the conclusion that it really is sufficient to align the scan bytes to the natural alignment of the *first* element. This would save us the `max()` comparisons for each bit. At the moment I am not at my workstation, but I could submit a v4 next Friday.
>>>>   
>>>
>>> I thought so too in the beginning, but as Jonathan pointed out, it does
>>> not work for all cases. Lets say you have u16,u16,u32,u16. If all
>>> channels are enabled the size is aligned to the first element, but the
>>> u32 would not be aligned in the second dataset.
>>>
>>
>> I'm sitting on this at the moment... Can I confirm we have consensus
>> that this patch is the correct fix?
>>
>> Lars and Lars?
> 
> Current version looks good to me.

I agree that the current implementation will fix the aforementioned cases.

> Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
> 
>>
>> Thanks,
>>
>> Jonathan
>>
>>
>>>>
>>>>   
>>>>> Fixes: 959d2952d124 ("staging:iio: make iio_sw_buffer_preenable much more
>>>>> general.")
>>>>> Signed-off-by: Lars Möllendorf <lars.moellendorf@plating.de>
>>>>> ---
>>>>> v3:
>>>>>   - Fix the problem description in the commit message
>>>>>   - Add "Fixes" tag
>>>>>
>>>>> v2:
>>>>>   - Fix subject of patch which marked it the first in a set of three.
>>>>>   - Add a description of the problem in the commit message
>>>>>
>>>>> ---
>>>>>  drivers/iio/industrialio-buffer.c | 6 +++++-
>>>>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
>>>>> index 5d05c38c4ba9..2f037cd59d53 100644
>>>>> --- a/drivers/iio/industrialio-buffer.c
>>>>> +++ b/drivers/iio/industrialio-buffer.c
>>>>> @@ -546,7 +546,7 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
>>>>>  				const unsigned long *mask, bool timestamp)
>>>>>  {
>>>>>  	unsigned bytes = 0;
>>>>> -	int length, i;
>>>>> +	int length, i, largest = 0;
>>>>>
>>>>>  	/* How much space will the demuxed element take? */
>>>>>  	for_each_set_bit(i, mask,
>>>>> @@ -554,13 +554,17 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
>>>>>  		length = iio_storage_bytes_for_si(indio_dev, i);
>>>>>  		bytes = ALIGN(bytes, length);
>>>>>  		bytes += length;
>>>>> +		largest = max(largest, length);
>>>>>  	}
>>>>>
>>>>>  	if (timestamp) {
>>>>>  		length = iio_storage_bytes_for_timestamp(indio_dev);
>>>>>  		bytes = ALIGN(bytes, length);
>>>>>  		bytes += length;
>>>>> +		largest = max(largest, length);
>>>>>  	}
>>>>> +
>>>>> +	bytes = ALIGN(bytes, largest);
>>>>>  	return bytes;
>>>>>  }
>>>>>
>>>>> --
>>>>> 2.23.0
>>>>>  
>>>
>>
> 

-- 

Lars Möllendorf, B. Eng.


Tel.:    +49 (0) 7641 93500-425
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E-Mail:  lars.moellendorf@plating.de <mailto:lars.moellendorf@plating.de>
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Re: [PATCH v3] iio: buffer: align the size of scan bytes to size of the largest element

[Jonathan Cameron]

On Fri, 27 Dec 2019 10:45:46 +0100
Lars Möllendorf <lars.moellendorf@plating.de> wrote:

> On 26.12.19 22:16, Lars-Peter Clausen wrote:
> > On 12/23/19 6:05 PM, Jonathan Cameron wrote:  
> >> On Mon, 16 Dec 2019 08:51:27 +0100
> >> Lars-Peter Clausen <lars@metafoo.de> wrote:
> >>  
> >>> On 12/15/19 10:09 PM, Lars Möllendorf wrote:  
> >>>> -----Ursprüngliche Nachricht-----    
> >>>>> Von: Lars Möllendorf <lars.moellendorf@plating.de>
> >>>>> Gesendet: Freitag 13 Dezember 2019 14:58
> >>>>> An: Jonathan Cameron <jic23@kernel.org>; Hartmut Knaack <knaack.h@gmx.de>; Lars-Peter Clausen <lars@metafoo.de>; Peter Meerwald-Stadler <pmeerw@pmeerw.net>; linux-iio@vger.kernel.org
> >>>>> CC: Lars Möllendorf <lars.moellendorf@plating.de>
> >>>>> Betreff: [PATCH v3] iio: buffer: align the size of scan bytes to size of the largest element
> >>>>>
> >>>>> Previous versions of `iio_compute_scan_bytes` only aligned each element
> >>>>> to its own length (i.e. its own natural alignment). Because multiple
> >>>>> consecutive sets of scan elements are buffered this does not work in
> >>>>> case the computed scan bytes do not align with the natural alignment of
> >>>>> the first scan element in the set.
> >>>>>
> >>>>> This commit fixes this by aligning the scan bytes to the natural
> >>>>> alignment of the largest scan element in the set.    
> >>>>
> >>>>
> >>>>
> >>>> After re-reading my commit message, I come to the conclusion that it really is sufficient to align the scan bytes to the natural alignment of the *first* element. This would save us the `max()` comparisons for each bit. At the moment I am not at my workstation, but I could submit a v4 next Friday.
> >>>>     
> >>>
> >>> I thought so too in the beginning, but as Jonathan pointed out, it does
> >>> not work for all cases. Lets say you have u16,u16,u32,u16. If all
> >>> channels are enabled the size is aligned to the first element, but the
> >>> u32 would not be aligned in the second dataset.
> >>>  
> >>
> >> I'm sitting on this at the moment... Can I confirm we have consensus
> >> that this patch is the correct fix?
> >>
> >> Lars and Lars?  
> > 
> > Current version looks good to me.  
> 
> I agree that the current implementation will fix the aforementioned cases.
Applied to the fixes-togreg branch of iio.git.  Hopefully
we won't have anyone relying on the previously broken alignment...

*crosses fingers*.

Thanks,

Jonathan

> 
> > Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
> >   
> >>
> >> Thanks,
> >>
> >> Jonathan
> >>
> >>  
> >>>>
> >>>>     
> >>>>> Fixes: 959d2952d124 ("staging:iio: make iio_sw_buffer_preenable much more
> >>>>> general.")
> >>>>> Signed-off-by: Lars Möllendorf <lars.moellendorf@plating.de>
> >>>>> ---
> >>>>> v3:
> >>>>>   - Fix the problem description in the commit message
> >>>>>   - Add "Fixes" tag
> >>>>>
> >>>>> v2:
> >>>>>   - Fix subject of patch which marked it the first in a set of three.
> >>>>>   - Add a description of the problem in the commit message
> >>>>>
> >>>>> ---
> >>>>>  drivers/iio/industrialio-buffer.c | 6 +++++-
> >>>>>  1 file changed, 5 insertions(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> >>>>> index 5d05c38c4ba9..2f037cd59d53 100644
> >>>>> --- a/drivers/iio/industrialio-buffer.c
> >>>>> +++ b/drivers/iio/industrialio-buffer.c
> >>>>> @@ -546,7 +546,7 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
> >>>>>  				const unsigned long *mask, bool timestamp)
> >>>>>  {
> >>>>>  	unsigned bytes = 0;
> >>>>> -	int length, i;
> >>>>> +	int length, i, largest = 0;
> >>>>>
> >>>>>  	/* How much space will the demuxed element take? */
> >>>>>  	for_each_set_bit(i, mask,
> >>>>> @@ -554,13 +554,17 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
> >>>>>  		length = iio_storage_bytes_for_si(indio_dev, i);
> >>>>>  		bytes = ALIGN(bytes, length);
> >>>>>  		bytes += length;
> >>>>> +		largest = max(largest, length);
> >>>>>  	}
> >>>>>
> >>>>>  	if (timestamp) {
> >>>>>  		length = iio_storage_bytes_for_timestamp(indio_dev);
> >>>>>  		bytes = ALIGN(bytes, length);
> >>>>>  		bytes += length;
> >>>>> +		largest = max(largest, length);
> >>>>>  	}
> >>>>> +
> >>>>> +	bytes = ALIGN(bytes, largest);
> >>>>>  	return bytes;
> >>>>>  }
> >>>>>
> >>>>> --
> >>>>> 2.23.0
> >>>>>    
> >>>  
> >>  
> >   
> 

[PATCH v3] iio: buffer: align the size of scan bytes to size of the largest element

[Lars Möllendorf]

Previous versions of `iio_compute_scan_bytes` only aligned each element
to its own length (i.e. its own natural alignment). Because multiple
consecutive sets of scan elements are buffered this does not work in
case the computed scan bytes do not align with the natural alignment of
the first scan element in the set.

This commit fixes this by aligning the scan bytes to the natural
alignment of the largest scan element in the set.

Fixes: 959d2952d124 ("staging:iio: make iio_sw_buffer_preenable much more general.")
Signed-off-by: Lars Möllendorf <lars.moellendorf@plating.de>
---
v3:
  - Fix the problem description in the commit message
  - Add "Fixes" tag

v2:
  - Fix subject of patch which marked it the first in a set of three.
  - Add a description of the problem in the commit message

---
 drivers/iio/industrialio-buffer.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
index 5d05c38c4ba9..2f037cd59d53 100644
--- a/drivers/iio/industrialio-buffer.c
+++ b/drivers/iio/industrialio-buffer.c
@@ -546,7 +546,7 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
 				const unsigned long *mask, bool timestamp)
 {
 	unsigned bytes = 0;
-	int length, i;
+	int length, i, largest = 0;

 	/* How much space will the demuxed element take? */
 	for_each_set_bit(i, mask,
@@ -554,13 +554,17 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
 		length = iio_storage_bytes_for_si(indio_dev, i);
 		bytes = ALIGN(bytes, length);
 		bytes += length;
+		largest = max(largest, length);
 	}

 	if (timestamp) {
 		length = iio_storage_bytes_for_timestamp(indio_dev);
 		bytes = ALIGN(bytes, length);
 		bytes += length;
+		largest = max(largest, length);
 	}
+
+	bytes = ALIGN(bytes, largest);
 	return bytes;
 }

--
2.23.0