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

Geert Uytterhoeven
2021-12-09T08:32:04Z

Hi Gabriel,

On Wed, Dec 8, 2021 at 9:14 PM Gabriel L. Somlo <gsomlo@gmail.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@linux-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