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

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Message-ID: <aWdoyCgLjjjaSbew@smile.fi.intel.com>
Date: Wed, 14 Jan 2026 11:58:32 +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 11:55:18AM +0200, 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.

Even more, since these devices are described in DT, the presence of any two
sequential windows will support my version for 100% correctness, as otherwise
it will mean overlapping in the addresses for two devices, i.e. 0x100 in one
is actually 0x00 in the other.

-- 
With Best Regards,
Andy Shevchenko