linux-kernel - Re: [PATCH 0/2] Extending PLL LUT for i.MX8MP Samsung HDMI PHY

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Message-ID: <ZuDjAwPxHeJTvXAp@atmark-techno.com>
Date: Wed, 11 Sep 2024 09:23:31 +0900
From: Dominique Martinet <dominique.martinet@...ark-techno.com>
To: Frieder Schrempf <frieder@...s.de>
Cc: Kishon Vijay Abraham I <kishon@...nel.org>,
	linux-kernel@...r.kernel.org, linux-phy@...ts.infradead.org,
	Vinod Koul <vkoul@...nel.org>, Adam Ford <aford173@...il.com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Marco Felsch <m.felsch@...gutronix.de>,
	Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Subject: Re: [PATCH 0/2] Extending PLL LUT for i.MX8MP Samsung HDMI PHY

Frieder Schrempf wrote on Tue, Sep 10, 2024 at 08:14:51PM +0200:
> [2] https://codeberg.org/fschrempf/samsung-hdmi-phy-pll-calculator/src/branch/main/pll.py

Great work! Thanks!

I was curious about the existing table entries, recomputing existing
values doesn't yield the same values. For example, the first entry is
{
        .pixclk = 22250000,
        .pll_div_regs = { 0xd1, 0x4b, 0xf1, 0x89, 0x88, 0x80, 0x40 },
}
but computing it yields
{
    .pixclk = 22250000,
    .pll_div_regs = { 0xd1, 0x4a, 0xf0, 0xef, 0x10, 0x81, 0x40 },
}

I assume there just are multiple ways to generate the same frequencies,
which is fine in itself, but it'd be great to be able to "back-compute"
the entries as a sanity check.

I've played a bit with your script and spent more time on it than I'd
like to admit, but something like this seems to do the trick, plugging
in the regs from the kernel:

---
pll = FractionalNPLL(freq_ref)

regs = [0xd1, 0x4b, 0xf1, 0x89, 0x88, 0x80, 0x40]
# assume fractional
if not regs[0] & 0xD0:
    print("reg[0] missing 0xD0")
    sys.exit(1)
pll.freq_frac = True
pll.params["p"] = regs[0] & 0x2f
pll.params["m"] = regs[1]
pll.params["s"] = (regs[2] >> 4) + 1
pll.params["n2"] = ((regs[2] >> 3) & 0x1) + 1
pll.params["n"] = (regs[2] & 0x7) + 4
pll.params["lc"] = regs[3] & 0x7f
if regs[4] & 0x80:
    pll.params["lc"] = - pll.params["lc"]
pll.params["k"] = regs[4] & 0x7f
pll.params["lc_s"] = regs[5] & 0x7f
pll.params["k_s"] = regs[6] & 0xbf


f_vco = int(pll.params["m"] * pll.f_ref / pll.params["p"])
if f_vco < 750000000 or f_vco > 3000000000:
    print(f"f_vco {f_vco} out of range")
    sys.exit(1)
f_calc = f_vco / pll.params["s"] / 5
pll.freq_int = round(f_calc)
print(f_calc)
sdc = pll.calc_sdc(pll.params)
frac = pll.calc_f_frac(sdc, pll.params)
print(frac)
freq = pll.freq_int + frac
print(freq)
pll.print_reg_driver_data(freq)
exit(0);
---
yields this back (comments added manually)
---
22500000.0 (integer part)
-250000.0 (fractional part)
22250000.0 (summed)

PHY Driver Table Entry:
{
    .pixclk = 22250000.0,
    .pll_div_regs = { 0xd1, 0x4b, 0xf1, 0x89, 0x88, 0x81, 0x40 },
}
---

so if I find some time I'll whip some loop to check all other values...




That aside, I see no problem with this, just one meta-comment about
adding a link to the script in an external repo: I see some other
drivers have python scripts in their trees e.g.
drivers/comedi/drivers/ni_routing/tools/*py
drivers/gpu/drm/ci/xfails/update-xfails.py
drivers/gpu/drm/msm/registers/gen_header.py

would it make sense to commit the script here instead of linking to a
repo that might be lost in the future?

I'm not quite sure what policy the linux repo has here, so leaving that
as an open question.
-- 
Dominique