> > +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!
>
> #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?
Regards,
Wolfram
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