linux-kernel - Re: [PATCH v5 07/10] i3c: master: Add driver for Cadence IP

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Date:   Wed, 11 Jul 2018 16:19:51 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Boris Brezillon <boris.brezillon@...tlin.com>
Cc:     Wolfram Sang <wsa@...-dreams.de>, linux-i2c@...r.kernel.org,
        Jonathan Corbet <corbet@....net>,
        "open list:DOCUMENTATION" <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>,
        DTML <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <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>
Subject: Re: [PATCH v5 07/10] i3c: master: Add driver for Cadence IP

On Fri, Jun 22, 2018 at 12:49 PM, Boris Brezillon
<boris.brezillon@...tlin.com> wrote:
> Add a driver for Cadence I3C master IP.

The driver seems very well-written and shows that the framework got that side
of the interface right. Just one thing I noticed:

> +
> +static void cdns_i3c_master_handle_ibi(struct cdns_i3c_master *master,
> +                                      u32 ibir)

> +
> +       for (i = 0; i < IBIR_XFER_BYTES(ibir); i += 4) {
> +               u32 tmp = readl(master->regs + IBI_DATA_FIFO);
> +
> +               for (j = 0; j < 4 && i + j < dev->ibi->max_payload_len; j++)
> +                       buf[i + j] = tmp >> (j * 8);
> +       }

This seems to be a rather inefficient way to open-code a readsl().
I suppose you need to handle length that is not a multiple of 4, right?

Maybe do it like

      size_t length = IBIR_XFER_BYTES(ibir);
      readsl(master->regs + IBI_DATA_FIFO, buf, length & ~3);
      if (length & 3) {
            u32 tmp = __raw_readl(master->regs + IBI_DATA_FIFO);
            memcpy(buf + length & ~3, length & 3);
      }

     Arnd