Hi Wolfram, On Tue, Jun 6, 2017 at 12:24 PM, Wolfram Sang <wsa@xxxxxxxxxxxxx> wrote: >> > +Therefore, it is *not* mandatory that the buffer of an i2c message is DMA safe. >> > +It does not seem reasonable to apply additional burdens when the feature is so >> > +rarely used. However, it is recommended to use a DMA-safe buffer, if your >> > +message size is likely applicable for DMA (FIXME: > 8 byte?). >> >> So you expect drivers to fall back to PIO automatically if the buffer is >> not DMA safe. Sounds good to me. > > Yes, I strongly recommend that. Otherwise, drivers can always deal with > bounce buffers on their own. > >> However, your check for a DMA-capable buffer is invoked only if >> CONFIG_DMA_API_DEBUG is enabled: > > is *NOT* enabled! Oops ;-) >> #if !defined(CONFIG_DMA_API_DEBUG) >> if (!virt_addr_valid(msg->buf) || object_is_on_stack(msg->buf)) { >> pr_debug("msg buffer to 0x%04x might not be DMA capable\n", >> msg->addr); >> return -EFAULT; >> } >> #endif >> > > The #if block is there because DMA_API_DEBUG does a lot more, but if the > check in the helper is enabled, the core will fall back to PIO and you > won't get the additional info from DMA_API_DEBUG. > > I think this needs a comment :) > > Now OK? So it won't fall back to PIO if CONFIG_DMA_API_DEBUG is enabled? 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 -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html