Re: [RFC PATCH v2 08/10] rtc: bd70528: Initial support for ROHM bd70528 RTC

From: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
To: Guenter Roeck <linux@roeck-us.net>
Cc: mazziesaccount@gmail.com, heikki.haikola@fi.rohmeurope.com,
	mikko.mutanen@fi.rohmeurope.com, lee.jones@linaro.org,
	robh+dt@kernel.org, mark.rutland@arm.com, broonie@kernel.org,
	gregkh@linuxfoundation.org, rafael@kernel.org,
	mturquette@baylibre.com, sboyd@kernel.org,
	linus.walleij@linaro.org, bgolaszewski@baylibre.com,
	sre@kernel.org, lgirdwood@gmail.com, a.zummo@towertech.it,
	alexandre.belloni@bootlin.com, wim@linux-watchdog.org,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-clk@vger.kernel.org, linux-gpio@vger.kernel.org,
	linux-pm@vger.kernel.org, linux-rtc@vger.kernel.org,
	linux-watchdog@vger.kernel.org
Subject: Re: [RFC PATCH v2 08/10] rtc: bd70528: Initial support for ROHM bd70528 RTC
Date: Mon, 28 Jan 2019 18:16:59 +0200	[thread overview]
Message-ID: <20190128161659.GA2121@localhost.localdomain> (raw)
In-Reply-To: <11ff93bf-c71f-7489-841f-09bf757a8ba7@roeck-us.net>

On Mon, Jan 28, 2019 at 06:02:47AM -0800, Guenter Roeck wrote:
> On 1/27/19 11:48 PM, Matti Vaittinen wrote:
> > Thanks again Guenter,
> > 
> > On Sat, Jan 26, 2019 at 08:30:24AM -0800, Guenter Roeck wrote:
> > > On 1/25/19 3:05 AM, Matti Vaittinen wrote:
> > > > +/*
> > > > + * We read regs RTC_SEC => RTC_YEAR
> > > > + * this struct is ordered according to chip registers.
> > > > + * Keep it u8 only to avoid padding issues.
> > > > + */
> > > > +struct bd70528_rtc_day {
> > > > +	u8 sec;
> > > > +	u8 min;
> > > > +	u8 hour;
> > > > +};
> > > > +
> > > > +struct bd70528_rtc_data {
> > > > +	struct bd70528_rtc_day time;
> > > > +	u8 week;
> > > > +	u8 day;
> > > > +	u8 month;
> > > > +	u8 year;
> > > > +};
> > > > +
> > > > +struct bd70528_rtc_wake {
> > > > +	struct bd70528_rtc_day time;
> > > > +	u8 ctrl;
> > > > +};
> > > > +
> > > > +struct bd70528_rtc_alm {
> > > > +	struct bd70528_rtc_data data;
> > > > +	u8 alm_mask;
> > > > +	u8 alm_repeat;
> > > > +};
> > > 
> > > At least some of the above are directly associated with chip registers.
> > > I don't think this will work for all architectures without explicit packed
> > > attribute.
> > 
> > Allright. I was thinking of that but thought that most of the
> > architectures using this PMIC would handle alignments fine if I used
> > only u8 members. I did consider using __attribute__((packed)) - but I'm
> > not sure if we hit into troubles with that too. I guess some people
> > would like to compile kernel with other compiler(s) but gcc - although
> > I'm not sure if this should be taken into account. I'll try doing some
> > study on this - unless someone replies to this and just tells how this
> > should be done. (I am pretty sure I can find the answer from mail
> > archives though). I'll try adding some packing hint for compiler at v3.
> > 
> 
> Use __packed ?

Right. That appends to __attribute__((packed)) on gcc. I'll use that.
Thanks for the tip :)

Br,
	Matti Vaittinen