Re: [PATCH v2 1/9] media: i2c: ov7251: Use in-range PLL1 dividers for the 319.2 MHz link

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Wed, Oct 28, 2026 at 08:21:46PM +0900, Antoine Pichot wrote:
> The 19.2 MHz PLL1 table for the 319.2 MHz link frequency puts a
> pre-divider of 1 before the multiplier of 133 and a divider of 4 after
> it, so the PLL1 multiplier output (the VCO) runs at 19.2 x 133 =
> 2553.6 MHz before being divided down to 638.4 MHz. The OV7750/OV7251
> datasheet (rev 2.12, table 2-11) limits it to 300 to 800 MHz.
> 
> Use pre-divider 4 (register 0x30B4 = 0x04) and divider 1 (0x30B1 =
> 0x01). The multiplier output is then 4.8 x 133 = 638.4 MHz, inside the
> range, and the MIPI clock stays 638.4 Mbps, so the link frequency does
> not change. The Windows driver programs these values for the Surface
> Book 2's Windows Hello mode.
> 
> On ACPI systems this table has been unreachable since it was added,
> because ov7251_check_hwcfg() selects the wrong index. The next patch
> fixes the index, so the two must go in together. With the index fix
> alone, a Surface Pro 7+ (IPU6) had CSI-2 errors in 7 of 10 150-frame
> runs, 3 of them stalls; with this change 0 of 13. A Surface Book 2
> (IPU3) streams clean with either table. Dave Stevenson measured on a
> 24 MHz Raspberry Pi board that the out-of-range tables miss their
> nominal frequency and proposed the same values. The 24 MHz tables are
> left alone because nobody in the thread can test a change to them.

> Fixes: ed9566ce1946 ("media: i2c: Add support for new frequencies to ov7251")
> Cc: stable@vger.kernel.org
> Link: https://lore.kernel.org/linux-media/6ae0e944.b6db0abd.16b13d.d261@mx.google.com/
> Link: https://lore.kernel.org/linux-media/CAPY8ntBFJJPg3y46gC=bNq_55QifC7mKmeq8+pAEDVN42fGUXw@mail.gmail.com/

These Links are not referred in the text above, make sure they are being
referred, otherwise Linus T. becomes grumpy on this. On top, consider
using Reported-by and Closes tags if applicable.

...

Code wise LGTM (I followed the discussion).

-- 
With Best Regards,
Andy Shevchenko