Re: [PATCH v8 07/10] i3c: master: Add driver for Cadence IP

From: Arnd Bergmann <arnd@arndb.de>
To: Boris Brezillon <boris.brezillon@bootlin.com>
Cc: Wolfram Sang <wsa@the-dreams.de>,
	Linux I2C <linux-i2c@vger.kernel.org>,
	Jonathan Corbet <corbet@lwn.net>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	gregkh <gregkh@linuxfoundation.org>,
	Przemyslaw Sroka <psroka@cadence.com>,
	Arkadiusz Golec <agolec@cadence.com>,
	Alan Douglas <adouglas@cadence.com>,
	Bartosz Folta <bfolta@cadence.com>, Damian Kos <dkos@cadence.com>,
	Alicja Jurasik-Urbaniak <alicja@cadence.com>,
	Cyprian Wronka <cwronka@cadence.com>,
	Suresh Punnoose <sureshp@cadence.com>,
	Rafal Ciepiela <rafalc@cadence.com>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Nishanth Menon <nm@ti.com>, Rob Herring <robh+dt@kernel.org>,
	Pawel Moll <pawel.moll@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Ian Campbell <ijc+devicetree@hellion.org.uk>,
	Kumar Gala <galak@codeaurora.org>,
	DTML <devicetree@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Vitor Soares <Vitor.Soares@synopsys.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	Xiang Lin <Xiang.Lin@synaptics.com>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	Sekhar Nori <nsekhar@ti.com>, Przemyslaw Gaj <pgaj@cadence.com>,
	Peter Rosin <peda@axentia.se>,
	mshettel@codeaurora.org, swboyd@chromium.org
Subject: Re: [PATCH v8 07/10] i3c: master: Add driver for Cadence IP
Date: Mon, 8 Oct 2018 12:06:30 +0200	[thread overview]
Message-ID: <CAK8P3a21t7pQ2uYWgu2+VZZNYc+pz_w3WCL7YVUEzqqyOFLvnA@mail.gmail.com> (raw)
In-Reply-To: <20181003132212.12619-8-boris.brezillon@bootlin.com>

On Wed, Oct 3, 2018 at 3:22 PM Boris Brezillon
<boris.brezillon@bootlin.com> wrote:
>
> Add a driver for Cadence I3C master IP.
>
> Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
> ---

> Changes in v7:
> - Fix readsl/writesl() usage
> - Add a depends on ARM || ARM64 || XTENSA to forbid selection of this
>   driver on platforms that are not implementing readsl/writesl

Most architectures include asm-generic/io.h, which contains a generic
implementation of readsl(). Maybe that #ifdef could be extended here?
I remember discussing this with you not so long ago, which led to
commit 0bbf47eab469 ("ia64: use asm-generic/io.h"). Do we have
a list of architectures that don't include asm-generic/io.h? Maybe
the 'depends on' could be for the set of architectures that fail here.

> +static void cdns_i3c_master_rd_from_rx_fifo(struct cdns_i3c_master *master,
> +                                           u8 *bytes, int nbytes)
> +{
> +       readsl(master->regs + RX_FIFO, bytes, nbytes / 4);
> +       if (nbytes & 3) {
> +               u32 tmp = __raw_readl(master->regs + RX_FIFO);
> +
> +               memcpy(bytes + (nbytes & ~3), &tmp, nbytes & 3);
> +       }
> +}

The __raw_readl() is probably correct here (I can't think of any
architecture on which it is not), but it still makes me feel uneasy
about possible endianess or other issues.

Maybe make this:?

        readsl(master->regs + RX_FIFO, &tmp, 1);

     Arnd