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

Gabriel L. Somlo
2021-12-08T20:14:35Z

Hi Geert,

I did *some* of this for v3, but since figured out how to use `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 */
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 */
};

Thanks again,
--Gabriel