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Date:   Fri, 18 Nov 2022 01:23:36 +0100
From:   Andrew Lunn <andrew@lunn.ch>
To:     Umang Jain <umang.jain@ideasonboard.com>
Cc:     Florian Fainelli <f.fainelli@gmail.com>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@broadcom.com>,
        Ray Jui <rjui@broadcom.com>, Dan Carpenter <error27@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Dave Stevenson <dave.stevenson@raspberrypi.com>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
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        kieran.bingham@ideasonboard.com
Subject: Re: [PATCH 2/3] vc04_services: mmal-vchiq: Use bool for
 vchiq_mmal_component.in_use
Message-ID: <Y3bQiDw11t4pRokP@lunn.ch>
References: <20221117160015.344528-1-umang.jain@ideasonboard.com>
 <20221117160015.344528-3-umang.jain@ideasonboard.com>
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>  struct vchiq_mmal_component {
> -	u32 in_use:1;
> +	bool in_use:1;
>  	bool enabled:1;

The patch you referenced says:

+If a structure has many true/false values, consider consolidating them into a
+bitfield with 1 bit members, or using an appropriate fixed width type, such as
+u8.

The code did exactly this, using two bits fields, in one u32. A bool
probably takes up 4 bytes, maybe 8 bytes, so this change probably
doubles the storage size for these two fields. Are these fields on the
hot path, where an extra AND instruction would make a difference?

    Andrew