On 10/31/23 10:46, Hans de Goede wrote:
> Hi Alain,
>
> On 10/30/23 18:36, Alain Volmat wrote:
>> Hi,
>>
>> Goal of this email is to get first comments prior to posting a patch.
>>
>> Could we consider enhancements within the v4l2-cci in order to also
>> allow regmap_range_cfg usage for paged register access ?
>
> Yes definitely.
>
> Extending v4l2-cci for other use cases was already briefly discussed
> between Kieran (Cc-ed) and me:
>
> The CCI part of the MIPI CSI spec says that multi-byte registers are
> always in big endian format, but some of the Sony IMX sensors actually
> use little-endian format for multi-byte registers.
>
> The main reason why we need v4l2-cci and cannot use regmap directly is
> because of the variable register width in CCI, where as regmap only
> supports a single width. v4l2 cci uses 8 bits width in the underlying
> regmap-config and then takes care of multy-byte registers by e.g.
> reading multiple bytes and calling e.g. get_unaligned_be16() on
> the read bytes.
>
> For the IMX scenario the plan is to add the notion of v4l2-cci
> flags by adding this to include/media/v4l2-cci.h :
>
> struct v4l2_cci {
> struct regmap *map;
> long flags;
> }
>
> And then change the prototype for devm_cci_regmap_init_i2c() to:
>
> struct v4l2_cci *devm_cci_regmap_init_i2c(struct i2c_client *client,
> int reg_addr_bits, long flags);
>
> And have devm_cci_regmap_init_i2c():
> 1. devm_kmalloc() a struct v4l2_cci
> 2. store the regmap there
> 3. copy over flags from the function argument
>
> Combined with modifying all the other functions to take
> "struct v4l2_cci *cci" as first argument instead of
> "struct regmap *map".
>
> This change will require all existing sensor drivers using
> v4l2-cci to be converted for the "struct regmap *map" ->
> "struct v4l2_cci *cci" change, this all needs to be done
> in one single commit adding the new struct + flags argument
> to avoid breaking the compilation.
>
> Then once we have this a second patch can add:
>
> /* devm_cci_regmap_init_i2c() flags argument defines */
> #define V4L2_CCI_DATA_LE BIT(0)
>
> to include/media/v4l2-cci.h and make v4l2-cci.h honor
> this flag solving the IMX scenario.
>
> We need to make this change sooner rather then later,
> while we only still have a few sensor drivers using
> v4l2-cci.
>
> So back to your question yes extensions are welcome
> and we already have one planned. If we are going to do
> more extensions though, then I really would want to see
> the little-endian data plan get implemented first, having
> our own struct v4l2_cci should help with future extensions
> were we can then just add more fields to it if necessary.
>
> I'm sorry about asking you to implement this first before
> being able to solve your own problem, but this should be
> relatively KISS to implement and I can test the patches
> for you for at least some of the sensor drivers.
>
>> At least two drivers currently being upstream and using v4l2-cci infrastructure
>> could benefit from regmap_range_cfg.
>> The GC0308 driver is partially using v4l2-cci and partially regmap (in order to use
>> regmap_range_cfg) and the GC2145 driver is using v4l2-cci but doing paging manually.
>>
>> The function devm_cci_regmap_init_i2c is already taking as parameter one argument
>> reg_addr_bits to be used in the regmap_config structure. We could also add
>> regmap_range_cfg pointer and size arguments to the function or
>> alternatively add another init function with more arguments ?
>
> I think adding a devm_cci_regmap_init_i2c_ex() would make sense here, this
> could already be done when adding the flags argument, giving only
> devm_cci_regmap_init_i2c_ex() the flags argument. For just the flags argument
> having a _ex seems overkill but if we are going to add regmap_range_cfg pointer
> and size arguments too then I think an _ex makes sense.
>
> And then in v4l2-cci.c only have the _ex and have a static inline helper
> in v4l2-cci-h defining the non _ex version ?
p.s.
To be clear if you like / plan to implement the devm_cci_regmap_init_i2c_ex()
variant, then this should be done in the first patch adding the:
struct v4l2_cci {
struct regmap *map;
long flags;
};
bits, so that we don't have to add an extra 0 argument for the flags to
all the existing callers of devm_cci_regmap_init_i2c() in that patch.
And then the IMX driver conversion can use the _ex variant.
Regards,
Hans
