Re: [PATCH v7 04/23] drm/i915/dsi: abstract intel_dsi_tlpx_ns()

[Jani Nikula <jani.nikula@intel.com>]

On Tue, 16 Oct 2018, Madhav Chauhan <madhav.chauhan@intel.com> wrote:
> On 10/15/2018 7:57 PM, Jani Nikula wrote:
>> Will be needed in the future. No functional changes.
>
> Agree, will be needing this while setting up DSI protocol timeouts for ICL.
>
>>
>> Cc: Madhav Chauhan <madhav.chauhan@intel.com>
>> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
>> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>> ---
>>   drivers/gpu/drm/i915/intel_dsi.c     | 13 +++++++++++++
>>   drivers/gpu/drm/i915/intel_dsi.h     |  1 +
>>   drivers/gpu/drm/i915/intel_dsi_vbt.c | 16 +---------------
>>   3 files changed, 15 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_dsi.c b/drivers/gpu/drm/i915/intel_dsi.c
>> index 4daa1da94047..a32cc1f4b384 100644
>> --- a/drivers/gpu/drm/i915/intel_dsi.c
>> +++ b/drivers/gpu/drm/i915/intel_dsi.c
>> @@ -15,3 +15,16 @@ int intel_dsi_bitrate(const struct intel_dsi *intel_dsi)
>>   
>>   	return intel_dsi->pclk * bpp / intel_dsi->lane_count;
>>   }
>> +
>> +int intel_dsi_tlpx_ns(const struct intel_dsi *intel_dsi)
>> +{
>> +	switch (intel_dsi->escape_clk_div) {
>> +	default:
>> +	case 0:
>> +		return 50;
>> +	case 1:
>> +		return 100;
>> +	case 2:
>> +		return 200;
>> +	}
>> +}
>
> Can we change the return of this function to unsigned int, there is no way
> that this function can return < 0  as per current implementation??

I'd rather not. I'm sure I should be able to justify this exhaustively
with examples, but I think gratuitous use of unsigned types leads to
issues with integer promotions and signed/unsigned comparisons etc. So
if it's "just a number", used for arithmetics, I'll pretty much choose
int every time.

And because you can silently assign negative numbers to unsigned types,
it's not a good safeguard to ensure positive numbers. Unless you're
happy with large positive numbers...

Unsigned types are best for register contents, bits, masks, etc.


BR,
Jani.


>
> Regards,
> Madhav
>
>> diff --git a/drivers/gpu/drm/i915/intel_dsi.h b/drivers/gpu/drm/i915/intel_dsi.h
>> index 68f14d8f1e18..0d911a4adfaa 100644
>> --- a/drivers/gpu/drm/i915/intel_dsi.h
>> +++ b/drivers/gpu/drm/i915/intel_dsi.h
>> @@ -131,6 +131,7 @@ static inline struct intel_dsi *enc_to_intel_dsi(struct drm_encoder *encoder)
>>   
>>   /* intel_dsi.c */
>>   int intel_dsi_bitrate(const struct intel_dsi *intel_dsi);
>> +int intel_dsi_tlpx_ns(const struct intel_dsi *intel_dsi);
>>   
>>   /* vlv_dsi.c */
>>   void vlv_dsi_wait_for_fifo_empty(struct intel_dsi *intel_dsi, enum port port);
>> diff --git a/drivers/gpu/drm/i915/intel_dsi_vbt.c b/drivers/gpu/drm/i915/intel_dsi_vbt.c
>> index fdeba8386d53..b0d8548f0462 100644
>> --- a/drivers/gpu/drm/i915/intel_dsi_vbt.c
>> +++ b/drivers/gpu/drm/i915/intel_dsi_vbt.c
>> @@ -512,21 +512,7 @@ static void vlv_dphy_param_init(struct intel_dsi *intel_dsi)
>>   	u32 lp_to_hs_switch, hs_to_lp_switch;
>>   	u32 mul;
>>   
>> -	switch (intel_dsi->escape_clk_div) {
>> -	case 0:
>> -		tlpx_ns = 50;
>> -		break;
>> -	case 1:
>> -		tlpx_ns = 100;
>> -		break;
>> -
>> -	case 2:
>> -		tlpx_ns = 200;
>> -		break;
>> -	default:
>> -		tlpx_ns = 50;
>> -		break;
>> -	}
>> +	tlpx_ns = intel_dsi_tlpx_ns(intel_dsi);
>>   
>>   	switch (intel_dsi->lane_count) {
>>   	case 1:
>

-- 
Jani Nikula, Intel Open Source Graphics Center
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