linux-kernel - Re: [PATCH v9 6/9] i3c: master: Add driver for Cadence IP

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Date:   Thu, 25 Oct 2018 18:07:20 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Wolfram Sang <wsa@...-dreams.de>, linux-i2c@...r.kernel.org,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Przemyslaw Sroka <psroka@...ence.com>,
        Arkadiusz Golec <agolec@...ence.com>,
        Alan Douglas <adouglas@...ence.com>,
        Bartosz Folta <bfolta@...ence.com>,
        Damian Kos <dkos@...ence.com>,
        Alicja Jurasik-Urbaniak <alicja@...ence.com>,
        Cyprian Wronka <cwronka@...ence.com>,
        Suresh Punnoose <sureshp@...ence.com>,
        Rafal Ciepiela <rafalc@...ence.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Nishanth Menon <nm@...com>, Rob Herring <robh+dt@...nel.org>,
        Pawel Moll <pawel.moll@....com>,
        Mark Rutland <mark.rutland@....com>,
        Ian Campbell <ijc+devicetree@...lion.org.uk>,
        Kumar Gala <galak@...eaurora.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Vitor Soares <Vitor.Soares@...opsys.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Xiang Lin <Xiang.Lin@...aptics.com>,
        linux-gpio@...r.kernel.org, Sekhar Nori <nsekhar@...com>,
        Przemyslaw Gaj <pgaj@...ence.com>,
        Peter Rosin <peda@...ntia.se>,
        Mike Shettel <mshettel@...eaurora.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Joe Perches <joe@...ches.com>
Subject: Re: [PATCH v9 6/9] i3c: master: Add driver for Cadence IP

On Thu, 25 Oct 2018 17:30:26 +0200
Arnd Bergmann <arnd@...db.de> wrote:

> On 10/24/18, Boris Brezillon <boris.brezillon@...tlin.com> wrote:
> > Hi Arnd,
> >
> > On Mon, 22 Oct 2018 15:34:01 +0200
> > Boris Brezillon <boris.brezillon@...tlin.com> wrote:
> >
> >  
> >> +
> >> +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);  
> >
> > Vitor reported a problem with readsl(): this function expects the 2nd
> > argument to be aligned on 32-bit, which is not guaranteed here. Unless
> > you see a better solution, I'll switch back to a loop doing:
> >
> > 	for (i = 0; i < nbytes; i += 4) {
> > 		u32 tmp = __raw_readl(...);
> > 		memcpy(bytes + i, &tmp,
> > 		       nbytes - i  > 4 ? 4 : nbytes - i);
> > 	}  
> 
> Could we maybe mandate that the buffer itself must be aligned here?
> What would be a reason why we see an unaligned target buffer?

Well, the buffers we pass to i3c_send_ccc_cmd() are not necessarily
aligned because they're not dynamically allocated (allocated on the
stack) and are not naturally aligned on 32-bits (either because they
are smaller than 32bits or because the struct is declared __packed).

I guess I could dynamically allocate the payload, but that requires
going over all users of i3c_send_ccc_cmd() to patch them.