linux-kernel - Re: [PATCH v7 05/10] nvmem: qcom-spmi-sdam: Migrate to devm_spmi_subdevice_alloc_and

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Message-ID: <aWdrS7poHyhTzyfN@smile.fi.intel.com>
Date: Wed, 14 Jan 2026 12:09:15 +0200
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	jic23@...nel.org, dlechner@...libre.com, nuno.sa@...log.com,
	andy@...nel.org, arnd@...db.de, gregkh@...uxfoundation.org,
	srini@...nel.org, vkoul@...nel.org, neil.armstrong@...aro.org,
	sre@...nel.org, sboyd@...nel.org, krzk@...nel.org,
	dmitry.baryshkov@....qualcomm.com, quic_wcheng@...cinc.com,
	melody.olvera@....qualcomm.com, quic_nsekar@...cinc.com,
	ivo.ivanov.ivanov1@...il.com, abelvesa@...nel.org,
	luca.weiss@...rphone.com, mitltlatltl@...il.com,
	krishna.kurapati@....qualcomm.com, linux-arm-msm@...r.kernel.org,
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-phy@...ts.infradead.org, linux-pm@...r.kernel.org,
	kernel@...labora.com
Subject: Re: [PATCH v7 05/10] nvmem: qcom-spmi-sdam: Migrate to
 devm_spmi_subdevice_alloc_and_add()

On Wed, Jan 14, 2026 at 11:04:30AM +0100, Konrad Dybcio wrote:
> On 1/14/26 10:55 AM, Andy Shevchenko wrote:
> > On Wed, Jan 14, 2026 at 10:47:20AM +0100, Konrad Dybcio wrote:
> >> On 1/14/26 10:42 AM, Andy Shevchenko wrote:
> >>> On Wed, Jan 14, 2026 at 10:09:45AM +0100, AngeloGioacchino Del Regno wrote:
> >>>> Il 14/01/26 10:07, Andy Shevchenko ha scritto:
> >>>>> On Wed, Jan 14, 2026 at 10:03:57AM +0100, AngeloGioacchino Del Regno wrote:
> >>>>>> Il 14/01/26 10:00, Andy Shevchenko ha scritto:
> >>>>>>> On Wed, Jan 14, 2026 at 09:59:40AM +0100, AngeloGioacchino Del Regno wrote:
> >>>>>>>> Il 14/01/26 09:56, Andy Shevchenko ha scritto:
> >>>>>>>>> On Wed, Jan 14, 2026 at 09:39:52AM +0100, AngeloGioacchino Del Regno wrote:

...

> >>>>>>>>>> +	struct regmap_config sdam_regmap_config = {
> >>>>>>>>>> +		.reg_bits = 16,
> >>>>>>>>>> +		.val_bits = 8,
> >>>>>>>>>
> >>>>>>>>>> +		.max_register = 0x100,
> >>>>>>>>>
> >>>>>>>>> Are you sure? This might be a bad naming, but here max == the last accessible.
> >>>>>>>>> I bet it has to be 0xff (but since the address is 16-bit it might be actually
> >>>>>>>>> 257 registers, but sounds very weird).
> >>>>>>>>
> >>>>>>>> Yes, I'm sure.
> >>>>>>>
> >>>>>>> So, what is resided on address 0x100 ?
> >>>>>>
> >>>>>> I don't remember, this is research from around 5 months ago, when I've sent
> >>>>>> the v1 of this.
> >>>>>>
> >>>>>> If you really want though, I can incorrectly set max_register to 0xff.
> >>>>>
> >>>>> Why incorrectly? Can you dig into the datasheet and check, please? We don't
> >>>>> know what is the 0x100 address means.
> >>>>
> >>>> I don't have any datasheets for Qualcomm IPs.
> >>>
> >>> Hmm... Can we have somebody from QC to check on this?
> >>> Perhaps Dmitry?
> >>
> >> 0xe6 is the last usable register today
> > 
> > Thanks for checking!
> > 
> >> But I wouldn't mind either 0xff or 0x100 because I don't want
> >> anyone to pull their hair out if a regmap access is dropped some day..
> > 
> > There is actually about the exact window size where registers are belong to the
> > same entity (subdevice). As in the HW world most of the things are stuck with
> > power-of-two numbers, and taking into account the naming of the field, I do not
> > believe one provides a 257 (256 + 1 = 2⁸ + 1) register _windows_ ("s" is also
> > important here, as it points out to the pattern) for the subdevices. I bet the
> > 0xff, i.e. 256, is the *correct* window from the HW perspective.
> 
> Right, [0x100n, 0x100n + 0xff] inclusive is the reserved register window
> for all Qualcomm PMIC peripherals, so I guess 0xff is the correct choice
> here

Thanks for the clarification, v8 addresses that, so seems to me good to go.

> If a peripheral is more complex, it's split into a couple of these
> same-sized blocks

Right.

-- 
With Best Regards,
Andy Shevchenko