[PATCH] media: rkisp1: uapi: change hist_bins array type from __u16 to __u32

[Dafna Hirschfeld]

Am 19.01.21 um 17:32 schrieb Hans Verkuil:
> On 19/01/2021 16:32, Dafna Hirschfeld wrote:
>>
>>
>> Am 19.01.21 um 16:00 schrieb Hans Verkuil:
>>> On 19/01/2021 15:53, Dafna Hirschfeld wrote:
>>>> Each entry in the array is a 20 bits value composed of 16
>>>> bits unsigned integer and 4 bits fractional part. So the
>>>> type should change to __u32.
>>>>
>>>> Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld at collabora.com>
>>>> ---
>>>> This patch is applied on top of v6 of the patchset
>>>> "Fix the rkisp1 userspace API for later IP versions"
>>>>
>>>>    include/uapi/linux/rkisp1-config.h | 5 +++--
>>>>    1 file changed, 3 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/include/uapi/linux/rkisp1-config.h b/include/uapi/linux/rkisp1-config.h
>>>> index 57ca3eea985f..47f6b84d7c56 100644
>>>> --- a/include/uapi/linux/rkisp1-config.h
>>>> +++ b/include/uapi/linux/rkisp1-config.h
>>>> @@ -895,7 +895,8 @@ struct rkisp1_cif_isp_af_stat {
>>>>    /**
>>>>     * struct rkisp1_cif_isp_hist_stat - statistics histogram data
>>>>     *
>>>> - * @hist_bins: measured bin counters
>>>> + * @hist_bins: measured bin counters. Each bin is a 20 bits value
>>>> + *	       composed of a 16-bit unsigned integer and 4 bits fractional part.
>>>
>>> So bits 0-3 are the fractional part and bits 4-19 contain the integer part?
>>> What goes where should be defined!
>>
>> Actually I don't know, I just copied the docs in the datasheet.
>> I can try figure it out. I can meanwhile send a patch without the doc until
>> we are sure. Is that OK?
> 
> No, this should be documented properly.

I see that indeed bits 0-3 are the fractional part.
The measurements are taken over 25 sub-windows and it is possible to
give a weight to each window. If I set all weights to 1 then I expect to get
an integer value and indeed in that case I see that the last 4 bits are always 0.
If I set the weights to other than 1 I get the last 4 bits not only 0.

The UAPI is generally not very good documented mainly because there is currently
no open source userspace that uses it.

> 
> Is this the only fractional type that is used in the rkisp1 uapi or are there
> others? (Just checking).

There are other places as well.
I see that there are some values in rkisp1_cif_isp_lsc_config that are fractional
and not documented.
The two other fractional types in the uapi are already documented.

I can add a patch that extends the documentation of all the fields in the uapi using the datasheet.
But I think such a patch can be added after de-staging.

Thanks,
Dafna


> 
>>
>>>
>>> Looking at rkisp1_stats_get_hst_meas() I see this:
>>>
>>>           for (i = 0; i < RKISP1_CIF_ISP_HIST_BIN_N_MAX; i++)
>>>                   pbuf->params.hist.hist_bins[i] =
>>>                           (u8)rkisp1_read(rkisp1,
>>>                                           RKISP1_CIF_ISP_HIST_BIN_0 + i * 4);
>>>
>>> Here this is cast to a u8, so how does this work?
>>
>> This seems to be a bug. I see that this cast is introduced in v12 of the patch
>> "media: staging: rkisp1: add capture device for statistics".
>> This cast does not exist in any of the downstream versions.
> 
> Clearly something that needs to be fixed as well.
> 
> Regards,
> 
> 	Hans
> 
>>
>> Thanks,
>> Dafna
>>
>>>
>>> There is something fishy here...
>>>
>>> Regards,
>>>
>>> 	Hans
>>>
>>>>     *
>>>>     * The histogram values divided into 16 bins for V10/V11 and 32 bins
>>>>     * for V12/V13. It is configured within the struct rkisp1_cif_isp_hst_config.
>>>> @@ -909,7 +910,7 @@ struct rkisp1_cif_isp_af_stat {
>>>>     * RKISP1_CIF_ISP_HIST_BIN_N_MAX is equal to the maximum of the two.
>>>>     */
>>>>    struct rkisp1_cif_isp_hist_stat {
>>>> -	__u16 hist_bins[RKISP1_CIF_ISP_HIST_BIN_N_MAX];
>>>> +	__u32 hist_bins[RKISP1_CIF_ISP_HIST_BIN_N_MAX];
>>>>    };
>>>>    
>>>>    /**
>>>>
>>>
>