Hi Michael,
On Wed, Mar 14, 2018 at 9:23 AM, Michael Schmitz <schmitzmic@xxxxxxxxx> wrote:
thanks for the review - largely uncontroversial except for the volatile...
The presence of volatile in drivers is always considered controversial ;-)
Am 14.03.2018 um 20:49 schrieb Geert Uytterhoeven:
+/* Blizzard 1230 DMA interface */
+
+struct blz1230_dma_registers {
+ volatile unsigned char dma_addr; /* DMA address [0x0000] */
volatile considered harmful.
Yes, I saw that. I also saw gcc miscompile the DMA set-up (in
particular, the case where three bytes of the transfer address are
stuffed consecutively into the same DMA address register).
If you would use proper *{read,write}*() accessors instead of direct
assignments,
you can drop the volatile's here.
Meaning writeb(val, reg) instead of reg = val?
#define out_8(addr,b) (void)((*(__force volatile u8 *) (addr)) = (b))
nicely hides the 'volatile' but suggests I also need to pass it a
pointer, so
writeb((addr >> 24) & 0xff, &dregs->dma_addr)
Yes, you have to pass it an (__iomem) pointer.
would do the same as
dregs->dma_addr = (addr >> 24) & 0xff; ??
Right.
I'll have to compare the assembly generated by the two versions before I
dare test that, but I'll give that a try. Liberal use of wmb() did fix
the miscompile but that just looked too ugly.
Using the macros should have the same effect due to the embedded volatile.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
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
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