On Wed, 28 Mar 2007, Tony Lindgren wrote:
> OK, attached is take #3 with ifndef CONFIG_HIGHMEM. Anybody have other
> limitations in mind?
> + /*
> + * Some systems need both transfer_buffer and transfer_dma
> + * to revert to PIO if DMA is temporarily unavailable.
> + * Note that transfer_buffer may not be accessible on some
> + * systems. In that case there is no need to use it either.
> + */
It would be nice if this comment were more grammatical. Consider this
instead:
/*
* Some systems can revert to PIO if DMA is temporarily
* unavailable; for their sake both transfer_buffer and
* transfer_dma must be set properly. However this is
* possible only on systems with no high memory, since
* DMA buffers located in high memory are not directly
* addressable by the kernel for PIO. When high memory
* is available, we NULL out transfer_buffer to avoid
* keeping a stale pointer and to help spot possible
* addressing bugs.
*/
> if (dma) {
> - /* hc may use _only_ transfer_dma */
> io->urbs [i]->transfer_dma = sg_dma_address (sg + i);
> len = sg_dma_len (sg + i);
> - } else {
> - /* hc may use _only_ transfer_buffer */
> +#ifndef CONFIG_HIGHMEM
> io->urbs [i]->transfer_buffer =
> page_address (sg [i].page) + sg [i].offset;
Insert here:
+#else
+ io->urbs[i]->transfer_buffer = NULL;
> +#endif
> + } else {
> len = sg [i].length;
> + io->urbs [i]->transfer_buffer =
> + page_address (sg [i].page) + sg [i].offset;
> }
Don't duplicate the old non-approved spacing style in new code. This
should say
+ io->urbs[i]->transfer_buffer =
+ page_address(sg[i].page) + sg[i].offset;
If you like, you can change the other occurrence of this to match.
Alan Stern
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