RE: [PATCH] mmc: tmio-mmc: fix bad pointer math

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Hi Geert,


On Tuesday, July 11, 2017, Geert Uytterhoeven wrote:
> > zeroing out the bottom 2 bits of count for out math.
> 
> s/out/our/

Thank you!

> > -               buf8 = (u8 *)(buf + (count >> 2));
> > +               buf8 = (u8 *)buf + (count & ~3);
> >                 count %= 4;
> 
> While correct, this is IMHO still difficult to understand for the casual
> reader.
> 
> Given the code before casts to "u32 *", and uses "count >>2", and the code
> after also casts to "u32 *", what about getting rid of all casts like:
> 
>         u32 data = 0;
>         u32 *buf32 = buf;
> 
>         if (is_read)
>                 sd_ctrl_read32_rep(host, CTL_SD_DATA_PORT, buf32,
>                                    count >> 2);
>         else
>                 sd_ctrl_write32_rep(host, CTL_SD_DATA_PORT, buf32,
>                                     count >> 2);
> 
>         /* if count was multiple of 4 */
>         if (!(count & 0x3))
>                 return;
> 
>         buf32 += count >> 2;
>         count %= 4;
> 
>         if (is_read) {
>                 sd_ctrl_read32_rep(host, CTL_SD_DATA_PORT, &data, 1);
>                 memcpy(buf32, &data, count);
>         } else {
>                 memcpy(&data, buf32, count);
>                 sd_ctrl_write32_rep(host, CTL_SD_DATA_PORT, &data, 1);
>         }
> 
>                 return;
>         }
> 

Good idea. I just tried it and it seems to work. I'll resend a patch.


>         u32 *buf32 = buf;

GCC didn't like this line without casting buf to a u32 *. It threw an 
error, not just a warning. Go figure.


Question:
>         u32 data = 0;

Any special reason why you are initializing this to 0????


Thank you,
Chris





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