Messages in this thread | | | Date | Mon, 19 Jun 2023 13:57:29 +0300 | Subject | Re: [PATCH v14 18/18] media: i2c: ds90ub953: Support non-sync mode | From | Tomi Valkeinen <> |
| |
On 19/06/2023 13:48, Andy Shevchenko wrote: > On Mon, Jun 19, 2023 at 12:00:57PM +0300, Tomi Valkeinen wrote: >> On 16/06/2023 17:47, Andy Shevchenko wrote: >>> On Fri, Jun 16, 2023 at 04:59:22PM +0300, Tomi Valkeinen wrote: >>>> Add support for FPD-Link non-sync mode with external clock. The only >>>> thing that needs to be added is the calculation for the clkout. > > ... > >>>> + switch (priv->mode) { >>>> + case UB953_MODE_SYNC: >>>> + if (priv->hw_data->is_ub971) >>>> + return priv->plat_data->bc_rate * 160ull; >>>> + else >>>> + return priv->plat_data->bc_rate / 2 * 160ull; >>> >>> Redundant 'else'. >> >> True, but I like the symmetry in: >> >> if (foo) >> return 123; >> else >> return 321; > > At the same time it will be symmetry with other switch-case(s). That's why the > question about fallthrough below. > >>> Do I understand correctly you don't want to fallthrough because it will give >>> ±160 in the rate (depending if it's even or odd)? >> >> Sorry, can you clarify? Fallthrough to what? > > To the below case since '/ 2 * 160 ~= *80'. Why ~ because it might give > off-by-one error due to even/odd input.
The below case is different. "priv->plat_data->bc_rate" vs "clk_get_rate(priv->clkin)".
As to the order of the calculation (/ 2 * 160 versus * 160 / 2), generally speaking, I have never figured out what are the correct ways to calculate clock rates.
I wrote "x / 2 * 160" as that's what the documentation gives (there's a hardware /2 divider in non-ub971 chips, followed by a 160 multiplier). But does the documentation presume that the calculation is done precisely, not in integers? If so, "x * 160 / 2" would be better (but then, do we need to round?). Or does the /2 hardware divider basically actually work as a an integer division, in case "x / 2 * 160" is the correct one.
>>>> + case UB953_MODE_NONSYNC_EXT: >>>> + /* CLKIN_DIV = 1 always */ >>>> + return clk_get_rate(priv->clkin) * 80ull; >
Tomi
| |