Re: [PATCH] fbtft: reduce stack usage

On Tue, Jun 10, 2025, at 12:26, Andy Shevchenko wrote:

On Tue, Jun 10, 2025 at 11:24:38AM +0200, Arnd Bergmann wrote:

quoted

Move the varargs handling into a separate noinline function so each
individual function stays below the limit. A better approach might be to
replace the varargs function with one that takes an array of arguments,
but that would be a much larger rework of the other callers.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

...

Thanks

quoted

+static noinline_for_stack void fbtft_write_register_64(struct fbtft_par *par,
+							int i, int buf[64])

Perhaps int i, int buf[64] should be u32?

Right, I can send an updated patch, or this could be fixed up when applying
the patch

quoted

+{
+	par->fbtftops.write_register(par, i,
+		buf[0], buf[1], buf[2], buf[3],
+		buf[4], buf[5], buf[6], buf[7],
+		buf[8], buf[9], buf[10], buf[11],
+		buf[12], buf[13], buf[14], buf[15],
+		buf[16], buf[17], buf[18], buf[19],
+		buf[20], buf[21], buf[22], buf[23],
+		buf[24], buf[25], buf[26], buf[27],
+		buf[28], buf[29], buf[30], buf[31],
+		buf[32], buf[33], buf[34], buf[35],
+		buf[36], buf[37], buf[38], buf[39],
+		buf[40], buf[41], buf[42], buf[43],
+		buf[44], buf[45], buf[46], buf[47],
+		buf[48], buf[49], buf[50], buf[51],
+		buf[52], buf[53], buf[54], buf[55],
+		buf[56], buf[57], buf[58], buf[59],
+		buf[60], buf[61], buf[62], buf[63]);
+}

Wondering if we may reuse this in other cases (by providing the additional
length parameter). But it may be done later on.

I tried this and that quickly became a mess. It is probably a good
idea to rework the code to completely avoid the varargs function
pointer and instead take an array here, but this is not something
I could easily do myself as that takes more time and needs better
testing.

       Arnd