linux-kernel - Re: [PATCH v2 3/3] mmc: Add driver for LiteX's LiteSDCard interface

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Date:   Thu, 9 Dec 2021 09:31:49 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     "Gabriel L. Somlo" <gsomlo@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Ulf Hansson <ulf.hansson@...aro.org>,
        Linux MMC List <linux-mmc@...r.kernel.org>,
        Karol Gugala <kgugala@...micro.com>,
        Mateusz Holenko <mholenko@...micro.com>,
        Kamil Rakoczy <krakoczy@...micro.com>,
        mdudek@...ernships.antmicro.com,
        Paul Mackerras <paulus@...abs.org>,
        Joel Stanley <joel@....id.au>,
        Stafford Horne <shorne@...il.com>,
        david.abdurachmanov@...ive.com,
        Florent Kermarrec <florent@...oy-digital.fr>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v2 3/3] mmc: Add driver for LiteX's LiteSDCard interface

Hi Gabriel,

On Wed, Dec 8, 2021 at 9:14 PM Gabriel L. Somlo <gsomlo@...il.com> wrote:
> I did *some* of this for v3, but since figured out how to use `pahole` :)

Right, pahole.

> On Mon, Dec 06, 2021 at 11:07:56AM +0100, Geert Uytterhoeven wrote:
> > > +struct litex_mmc_host {
> > > +       struct mmc_host *mmc;
> > > +       struct platform_device *dev;
> > > +
> > > +       void __iomem *sdphy;
> > > +       void __iomem *sdcore;
> > > +       void __iomem *sdreader;
> > > +       void __iomem *sdwriter;
> > > +       void __iomem *sdirq;
> > > +
> > > +       u32 resp[4];
> > > +       u16 rca;
> > > +
> > > +       void *buffer;
> > > +       size_t buf_size;
> > > +       dma_addr_t dma;
> > > +
> > > +       unsigned int freq;
> > > +       unsigned int clock;
> > > +       bool is_bus_width_set;
> > > +       bool app_cmd;
> > > +
> > > +       int irq;
> > > +       struct completion cmd_done;
> >
> > You may want to reorder the members to avoid implicit gaps
> > (i.e. structs first, followed by integral types in decreasing size).
>
> So, for v4, I'll have it looking like this, which `pahole` says is
> optimally packed:
>
> struct litex_mmc_host {
>         struct mmc_host *          mmc;                  /*     0     8 */
>         struct platform_device *   dev;                  /*     8     8 */
>         void *                     sdphy;                /*    16     8 */
>         void *                     sdcore;               /*    24     8 */
>         void *                     sdreader;             /*    32     8 */
>         void *                     sdwriter;             /*    40     8 */
>         void *                     sdirq;                /*    48     8 */
>         void *                     buffer;               /*    56     8 */
>         /* --- cacheline 1 boundary (64 bytes) --- */
>         size_t                     buf_size;             /*    64     8 */

size_t is 32-bit on RV32, so you may want to move it below cmd_done.

>         dma_addr_t                 dma;                  /*    72     8 */
>         struct completion          cmd_done;             /*    80    32 */
>         int                        irq;                  /*   112     4 */
>         unsigned int               ref_clk;              /*   116     4 */
>         unsigned int               sd_clk;               /*   120     4 */
>         u32                        resp[4];              /*   124    16 */
>         /* --- cacheline 2 boundary (128 bytes) was 12 bytes ago --- */
>         u16                        rca;                  /*   140     2 */
>         bool                       is_bus_width_set;     /*   142     1 */
>         bool                       app_cmd;              /*   143     1 */
>
>         /* size: 144, cachelines: 3, members: 18 */
>         /* last cacheline: 16 bytes */
> };

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds