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Message-ID: <3dc83aa5c1d138ef70dd64ba4154acb52b65a8a3.camel@gmail.com>
Subject: Re: [PATCH v3 6/6] iio: adc: ad7173: Reduce device info struct size
From: Nuno =?ISO-8859-1?Q?S=E1?= <noname.nuno@gmail.com>
To: David Lechner <dlechner@baylibre.com>, dumitru.ceclan@analog.com
Cc: Lars-Peter Clausen <lars@metafoo.de>, Michael Hennerich
 <Michael.Hennerich@analog.com>, Jonathan Cameron <jic23@kernel.org>, Rob
 Herring <robh@kernel.org>, Krzysztof Kozlowski
 <krzysztof.kozlowski+dt@linaro.org>, Conor Dooley <conor+dt@kernel.org>,
 linux-iio@vger.kernel.org, devicetree@vger.kernel.org, 
 linux-kernel@vger.kernel.org, Dumitru Ceclan <mitrutzceclan@gmail.com>
Date: Thu, 30 May 2024 08:17:47 +0200
In-Reply-To: <ec2ac6fb-0f08-4e8c-8907-83bd8f0976c8@baylibre.com>
References: <20240527-ad4111-v3-0-7e9eddbbd3eb@analog.com>
	 <20240527-ad4111-v3-6-7e9eddbbd3eb@analog.com>
	 <2f26b72970be841279ca00c1b5eb91dcfffabdea.camel@gmail.com>
	 <ec2ac6fb-0f08-4e8c-8907-83bd8f0976c8@baylibre.com>
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On Wed, 2024-05-29 at 15:32 -0500, David Lechner wrote:
> On 5/29/24 7:23 AM, Nuno S=C3=A1 wrote:
> > On Mon, 2024-05-27 at 20:02 +0300, Dumitru Ceclan via B4 Relay wrote:
> > > From: Dumitru Ceclan <dumitru.ceclan@analog.com>
> > >=20
> > > Reduce the size used by the device info struct by packing the bool
> > > =C2=A0fields within the same byte. This reduces the struct size from =
52 bytes
> > > =C2=A0to 44 bytes.
> > >=20
> > > Signed-off-by: Dumitru Ceclan <dumitru.ceclan@analog.com>
> > > ---
> > > =C2=A0drivers/iio/adc/ad7173.c | 16 ++++++++--------
> > > =C2=A01 file changed, 8 insertions(+), 8 deletions(-)
> > >=20
> > > diff --git a/drivers/iio/adc/ad7173.c b/drivers/iio/adc/ad7173.c
> > > index 328685ce25e0..e8357a21d513 100644
> > > --- a/drivers/iio/adc/ad7173.c
> > > +++ b/drivers/iio/adc/ad7173.c
> > > @@ -179,15 +179,15 @@ struct ad7173_device_info {
> > > =C2=A0	unsigned int clock;
> > > =C2=A0	unsigned int id;
> > > =C2=A0	char *name;
> > > -	bool has_current_inputs;
> > > -	bool has_vcom_input;
> > > -	bool has_temp;
> > > +	bool has_current_inputs		:1;
> > > +	bool has_vcom_input		:1;
> > > +	bool has_temp			:1;
> > > =C2=A0	/* ((AVDD1 =E2=88=92 AVSS)/5) */
> > > -	bool has_common_input;
> > > -	bool has_input_buf;
> > > -	bool has_int_ref;
> > > -	bool has_ref2;
> > > -	bool higher_gpio_bits;
> > > +	bool has_common_input		:1;
> > > +	bool has_input_buf		:1;
> > > +	bool has_int_ref		:1;
> > > +	bool has_ref2			:1;
> > > +	bool higher_gpio_bits		:1;
> > > =C2=A0	u8 num_gpios;
> > > =C2=A0};
> > > =C2=A0
> > >=20
> >=20
> > This is really a very micro optimization... I would drop it tbh but no =
strong
> > feelings about it.
> >=20
> > - Nuno S=C3=A1
>=20
> This only considers RAM size and not code size too. At least on ARM arch
> every time we read or write to one of these fields, the code is now
> implicitly `((field & 0x1) >> bits)` so two extra assembly instructions
> for each read and write. This could be bigger than the size saved in
> the structs.
>=20
>=20

very good point...

- Nuno S=C3=A1