linux-kernel - Re: [PATCH 6/7] iio: adc: ad485x: add ad485x driver

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Message-ID: <Zv5zj0PFhxoeBUXQ@smile.fi.intel.com>
Date: Thu, 3 Oct 2024 13:35:59 +0300
From: Andy Shevchenko <andy@...nel.org>
To: "Miclaus, Antoniu" <Antoniu.Miclaus@...log.com>
Cc: David Lechner <dlechner@...libre.com>,
	Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	"Hennerich, Michael" <Michael.Hennerich@...log.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, "Sa, Nuno" <Nuno.Sa@...log.com>,
	Olivier Moysan <olivier.moysan@...s.st.com>,
	Uwe Kleine-König <ukleinek@...nel.org>,
	"Schmitt, Marcelo" <Marcelo.Schmitt@...log.com>,
	João Paulo Gonçalves <joao.goncalves@...adex.com>,
	Mike Looijmans <mike.looijmans@...ic.nl>,
	Dumitru Ceclan <mitrutzceclan@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Alisa-Dariana Roman <alisadariana@...il.com>,
	"Cuciurean, Sergiu" <Sergiu.Cuciurean@...log.com>,
	"Bogdan, Dragos" <Dragos.Bogdan@...log.com>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>
Subject: Re: [PATCH 6/7] iio: adc: ad485x: add ad485x driver

On Thu, Oct 03, 2024 at 10:14:57AM +0000, Miclaus, Antoniu wrote:
> > On 10/1/24 8:51 AM, Miclaus, Antoniu wrote:
> > >>> Regarding the bulk writes/reads, the msb/mid/lsb registers need to be
> > >>> read/write in a specific order and the addresses are not incremental,
> > >>
> > >> We have _noinc() variants of regmap accessors.
> > > [Miclaus, Antoniu]
> > > I think _noinc() functions read from the same register address so it doesn't
> > > apply.
> > > I am reading values from multiple register addresses that are not reg_addr,
> > > reg_addr+1, reg_addr+2.
> > 
> > I'm confused by the statement that the registers are not incremental.
> > 
> > For example, this patch defines...
> > 
> > +#define AD485X_REG_CHX_OFFSET_LSB(ch)
> > 	AD485X_REG_CHX_OFFSET(ch)
> > +#define AD485X_REG_CHX_OFFSET_MID(ch)
> > 	(AD485X_REG_CHX_OFFSET_LSB(ch) + 0x01)
> > +#define AD485X_REG_CHX_OFFSET_MSB(ch)
> > 	(AD485X_REG_CHX_OFFSET_MID(ch) + 0x01)
> > 
> > This looks exactly like reg_addr, reg_addr+1, reg_addr+2 to me.
> Yes you are right. Although I tested with hardware and it seems that the registers
> are not properly written when using bulk operations. My guess is that holding CS low during
> the entire transaction might be a possible issue. Any suggestions are appreciated.

Okay, so each byte has to be written as a separate SPI transfer?
I believe we have already examples of the drivers for such a hardware
in the Linux kernel, but I can't throw any example form top of my head.

> > >>> so I am not sure how the bulk functions fit. On this matter, we will need
> > >>> unsigned int (not u8) to store the values read via regmap_read, and in this
> > >>> case we will need extra casts and assignments to use get_unaligned.

-- 
With Best Regards,
Andy Shevchenko