linux-kernel - Re: [PATCH v5 1/4] virtio_rtc: Add module and driver core

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Message-ID: <uj7g35pvelxwnukbkii6d7kzc4pjsj6wrtbcuomg3vhdluoxap@owoy3uy3xcrr>
Date: Tue, 25 Feb 2025 13:25:53 +0100
From: Peter Hilber <quic_philber@...cinc.com>
To: Simon Horman <horms@...nel.org>
CC: "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        Srivatsa Vaddagiri
	<quic_svaddagi@...cinc.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Eugenio
 Pérez <eperezma@...hat.com>,
        Richard Cochran
	<richardcochran@...il.com>,
        <linux-kernel@...r.kernel.org>, <virtualization@...ts.linux.dev>,
        <netdev@...r.kernel.org>, David Woodhouse
	<dwmw2@...radead.org>,
        "Ridoux, Julien" <ridouxj@...zon.com>, Marc Zyngier
	<maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Daniel Lezcano
	<daniel.lezcano@...aro.org>,
        Alexandre Belloni
	<alexandre.belloni@...tlin.com>,
        Parav Pandit <parav@...dia.com>,
        "Matias
 Ezequiel Vara Larsen" <mvaralar@...hat.com>,
        Cornelia Huck
	<cohuck@...hat.com>, <virtio-dev@...ts.linux.dev>,
        <linux-arm-kernel@...ts.infradead.org>, <linux-rtc@...r.kernel.org>
Subject: Re: [PATCH v5 1/4] virtio_rtc: Add module and driver core

On Mon, Feb 24, 2025 at 05:55:27PM +0000, Simon Horman wrote:
> On Wed, Feb 19, 2025 at 08:32:56PM +0100, Peter Hilber wrote:
> 
> ...
> 
> > +/**
> > + * VIORTC_MSG() - extract message from message handle
> > + * @hdl: message handle
> > + *
> > + * Return: struct viortc_msg
> > + */
> > +#define VIORTC_MSG(hdl) ((hdl).msg)
> > +
> > +/**
> > + * VIORTC_MSG_INIT() - initialize message handle
> > + * @hdl: message handle
> > + * @viortc: device data (struct viortc_dev *)
> > + *
> > + * Context: Process context.
> > + * Return: 0 on success, -ENOMEM otherwise.
> > + */
> > +#define VIORTC_MSG_INIT(hdl, viortc)                                         \
> > +	({                                                                   \
> > +		typeof(hdl) *_hdl = &(hdl);                                  \
> > +									     \
> > +		_hdl->msg = viortc_msg_init((viortc), _hdl->msg_type,        \
> > +					    _hdl->req_size, _hdl->resp_cap); \
> > +		if (_hdl->msg) {                                             \
> > +			_hdl->req = _hdl->msg->req;                          \
> > +			_hdl->resp = _hdl->msg->resp;                        \
> > +		}                                                            \
> > +		_hdl->msg ? 0 : -ENOMEM;                                     \
> > +	})
> > +
> > +/**
> > + * VIORTC_MSG_WRITE() - write a request message field
> > + * @hdl: message handle
> > + * @dest_member: request message field name
> > + * @src_ptr: pointer to data of compatible type
> > + *
> > + * Writes the field in little-endian format.
> > + */
> > +#define VIORTC_MSG_WRITE(hdl, dest_member, src_ptr)                         \
> > +	do {                                                                \
> > +		typeof(hdl) _hdl = (hdl);                                   \
> > +		typeof(src_ptr) _src_ptr = (src_ptr);                       \
> > +									    \
> > +		/* Sanity check: must match the member's type */            \
> > +		typecheck(typeof(_hdl.req->dest_member), *_src_ptr);        \
> 
> Hi Peter,
> 
> FWIIW, this trips up sparse because from it's perspective
> there is an endianness mismatch between the two types.
> 

Thanks, I took a closer look and I think a virtio_le_to_cpu() inside the
typeof()s will both keep the sanity check working and keep sparse from
complaining - in the below case as well.

Peter

> > +									    \
> > +		_hdl.req->dest_member =                                     \
> > +			virtio_cpu_to_le(*_src_ptr, _hdl.req->dest_member); \
> > +	} while (0)
> > +
> > +/**
> > + * VIORTC_MSG_READ() - read from a response message field
> > + * @hdl: message handle
> > + * @src_member: response message field name
> > + * @dest_ptr: pointer to data of compatible type
> > + *
> > + * Converts from little-endian format and writes to dest_ptr.
> > + */
> > +#define VIORTC_MSG_READ(hdl, src_member, dest_ptr)                     \
> > +	do {                                                           \
> > +		typeof(dest_ptr) _dest_ptr = (dest_ptr);               \
> > +								       \
> > +		/* Sanity check: must match the member's type */       \
> > +		typecheck(typeof((hdl).resp->src_member), *_dest_ptr); \
> 
> Ditto.
> 
> > +								       \
> > +		*_dest_ptr = virtio_le_to_cpu((hdl).resp->src_member); \
> > +	} while (0)
> > +
> > +/*
> > + * read requests
> > + */
> 
> ...