Re: [PATCH net-next 1/7] page_pool: disable dma mapping support for 32-bit arch with 64-bit DMA

Hi Jesper,

On Thu, 23 Sept 2021 at 12:33, Jesper Dangaard Brouer
[off-list ref] wrote:

On 22/09/2021 11.41, Yunsheng Lin wrote:

quoted

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 1a6978427d6c..a65bd7972e37 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c

@@ -49,6 +49,12 @@ static int page_pool_init(struct page_pool *pool,
       * which is the XDP_TX use-case.
       */
      if (pool->p.flags & PP_FLAG_DMA_MAP) {
+             /* DMA-mapping is not supported on 32-bit systems with
+              * 64-bit DMA mapping.
+              */
+             if (sizeof(dma_addr_t) > sizeof(unsigned long))
+                     return -EINVAL;

As I said before, can we please use another error than EINVAL.
We should give drivers a chance/ability to detect this error, and e.g.
fallback to doing DMA mappings inside driver instead.

I suggest using EOPNOTSUPP 95 (Operation not supported).

I am fine with both.  In any case though the aforementioned driver can
just remove PP_FLAG_DMA_MAP and do it's own mappings.

Regards
/Ilias

-Jesper