[U-Boot] [RFC PATCH] Pre-console buffer for ARM

[Wolfgang Denk]

Dear Graeme Russ,

In message <CALButCJF1p+60WOLtiJqhcAed-71VxmP2mBqY2wdNURPk5=Q+g at mail.gmail.com> you wrote:
> 
> >> > it's fairly easy as well:
> >> > #define CIRC_BUF_IDX(idx) ((idx) & (CONFIG_SYS_TMP_CON_BUF_SZ-1))
> >> > buffer[CIRC_BUF_IDX(gd->conf_buf_idx++)] = c;
> >>
> >> But does that work for non power-of-two buffer sizes...
> >
> > no, but not that big of a deal.  so you get limited to the last 1KiB, 4KiB,
> > 8KiB, 16KiB, etc... amount of data.
> 
> Until someone doesn't read the documentation and figures they can only
> squeeze 200 bytes out of their L1 cache after making room for gd and stack
> and then tries to print 201 bytes of debug info and trashes either the
> stack or gd and then things start to get a lot weirder than simply having
> their early debug messgaes clipped...
> 
> To be safe, CONFIG_SYS_TMP_CON_BUF_SZ would need to be checked for ^2 size
> and now we only get 128 bytes rather than 200 :( - Better to add another
> long in gd and get 196

Grrrgh.

If you want to support arbitrary buffer sizes, then just use

	#define CIRC_BUF_IDX(idx) ((idx) % CONFIG_SYS_TMP_CON_BUF_SZ)

Best regards,

Wolfgang Denk

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