linux-kernel - [PATCH net-next -v5 1/4] page_pool: disable dma mapping support for 32-bit arch with 64-bit DMA

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Date:   Sat, 9 Oct 2021 17:37:21 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     <davem@...emloft.net>, <kuba@...nel.org>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linuxarm@...neuler.org>, <akpm@...ux-foundation.org>,
        <hawk@...nel.org>, <ilias.apalodimas@...aro.org>,
        <peterz@...radead.org>, <yuzhao@...gle.com>, <jhubbard@...dia.com>,
        <will@...nel.org>, <willy@...radead.org>, <jgg@...pe.ca>,
        <mcroce@...rosoft.com>, <willemb@...gle.com>,
        <cong.wang@...edance.com>, <pabeni@...hat.com>,
        <haokexin@...il.com>, <nogikh@...gle.com>, <elver@...gle.com>,
        <memxor@...il.com>, <vvs@...tuozzo.com>, <linux-mm@...ck.org>,
        <edumazet@...gle.com>, <alexander.duyck@...il.com>,
        <dsahern@...il.com>
Subject: [PATCH net-next -v5 1/4] page_pool: disable dma mapping support for 32-bit arch with 64-bit DMA

As the 32-bit arch with 64-bit DMA seems to rare those days,
and page pool is carrying a lot of code and complexity for
systems that possibly don't exist when the pp page frag
tracking support is added.

So disable dma mapping support for such systems, if drivers
really want to work on such systems, they have to implement
their own DMA-mapping fallback tracking outside page_pool.

Reviewed-by: Ilias Apalodimas <ilias.apalodimas@...aro.org>
Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
---
 include/linux/mm_types.h | 13 +------------
 include/net/page_pool.h  | 12 +-----------
 net/core/page_pool.c     | 10 ++++++----
 3 files changed, 8 insertions(+), 27 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 7f8ee09c711f..436e0946d691 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -104,18 +104,7 @@ struct page {
 			struct page_pool *pp;
 			unsigned long _pp_mapping_pad;
 			unsigned long dma_addr;
-			union {
-				/**
-				 * dma_addr_upper: might require a 64-bit
-				 * value on 32-bit architectures.
-				 */
-				unsigned long dma_addr_upper;
-				/**
-				 * For frag page support, not supported in
-				 * 32-bit architectures with 64-bit DMA.
-				 */
-				atomic_long_t pp_frag_count;
-			};
+			atomic_long_t pp_frag_count;
 		};
 		struct {	/* slab, slob and slub */
 			union {
diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index a4082406a003..3855f069627f 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -216,24 +216,14 @@ static inline void page_pool_recycle_direct(struct page_pool *pool,
 	page_pool_put_full_page(pool, page, true);
 }
 
-#define PAGE_POOL_DMA_USE_PP_FRAG_COUNT	\
-		(sizeof(dma_addr_t) > sizeof(unsigned long))
-
 static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
 {
-	dma_addr_t ret = page->dma_addr;
-
-	if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT)
-		ret |= (dma_addr_t)page->dma_addr_upper << 16 << 16;
-
-	return ret;
+	return page->dma_addr;
 }
 
 static inline void page_pool_set_dma_addr(struct page *page, dma_addr_t addr)
 {
 	page->dma_addr = addr;
-	if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT)
-		page->dma_addr_upper = upper_32_bits(addr);
 }
 
 static inline void page_pool_set_frag_count(struct page *page, long nr)
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 1a6978427d6c..9b60e4301a44 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 -EOPNOTSUPP;
+
 		if ((pool->p.dma_dir != DMA_FROM_DEVICE) &&
 		    (pool->p.dma_dir != DMA_BIDIRECTIONAL))
 			return -EINVAL;
@@ -69,10 +75,6 @@ static int page_pool_init(struct page_pool *pool,
 		 */
 	}
 
-	if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT &&
-	    pool->p.flags & PP_FLAG_PAGE_FRAG)
-		return -EINVAL;
-
 	if (ptr_ring_init(&pool->ring, ring_qsize, GFP_KERNEL) < 0)
 		return -ENOMEM;
 
-- 
2.33.0