Re: [PATCH v3 2/4] media: mali-c55: Implement CCM block validation

[Vincenzo Frascino]

Hello Laurent,

On 29/06/2026 10:57, Laurent Pinchart wrote:
> Hi Jacopo,
> 
> Thank you for the patch.
> 
> On Sat, Jun 27, 2026 at 04:29:14PM +0200, Jacopo Mondi wrote:
>> From: Jacopo Mondi <jacopo.mondi+renesas@xxxxxxxxxxxxxxxx>
>>
>> Implement validation of CCM block parameters.
>>
>> CCM coefficients are expressed as 13 bits signed Q4.8 format and their
>> raw value cannot be higher than 8191 (BIT(13) - 1).
>>
>> CCM gains are expressed as unsigned 12 bits Q4.8 format and their raw
>> value cannot be higher than 4095 (BIT(12) - 1).
>>
>> CCM offsets are 12 bits unsigned integers and their value cannot be
>> higher than 4095 (BIT(12) - 1).
>>
>> Validate the parameters provided by userspace using the .block_validate
>> callback of struct v4l2_isp_params_block_type_info.
> I don't think this is needed.
> 
> We need to validate parameters that can cause the ISP to malfunction in
> ways that requires a system reset, or in ways that cause malfunction of
> other system components (e.g. buffer overflows, memory bus lock ups,
> ...). The rest doesn't need to be validated.
> 
> If you want to be cautious, you can just mask the value when writing to
> registers, which I think you're doing in patch 1/4.

According to me here is not a matter of being cautious, but of honouring the
contract with the userspace.

If the userspace is doing something wrong it should be notified. The only
reasonable argument against this would be if this code is on a critical path and
the validations have a performance impact.

@Jacopo, can you please confirm if this is the case?


-- 
Regards,
Vincenzo