apm821xx: fix dmesg warning slop

Fix by replacing memset with manual 0 assignments. The first patch was
rightly rejected by upstream as it affects everything so keep it in 9xx.

Upstream message for it is:

dcbz instruction shouldn't be used on non-cached memory. Using
it on non-cached memory can result in alignment exception and
implies a heavy handling.

Instead of silentely emulating the instruction and resulting in high
performance degradation, warn whenever an alignment exception is
taken in kernel mode due to dcbz, so that the user is made aware that
dcbz instruction has been used unexpectedly by the kernel.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/23382
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>

target/linux/apm821xx/patches-6.18/700-net-ibm-emac-Clear-MAL-descriptors-without-memset.patch

@@ -0,0 +1,49 @@
+From f992336a598ce4508b75e25dff755715f38b9b8e Mon Sep 17 00:00:00 2001
+From: Rosen Penev <rosenp@gmail.com>
+Date: Sat, 16 May 2026 16:31:09 -0700
+Subject: [PATCH] net: ibm: emac: Clear MAL descriptors without memset
+
+Clear MAL descriptor rings with explicit field stores instead of
+memset().  The descriptor rings are carved from MAL coherent DMA memory,
+which may be mapped uncached on 32-bit powerpc.  The optimized memset()
+path can use dcbz there and trigger an alignment warning.
+
+The skb tracking arrays remain ordinary CPU memory and still use memset().
+
+Assisted-by: Codex:GPT-5.5
+Signed-off-by: Rosen Penev <rosenp@gmail.com>
+---
+ drivers/net/ethernet/ibm/emac/core.c | 15 +++++++++++++--
+ 1 file changed, 13 insertions(+), 2 deletions(-)
+
+--- a/drivers/net/ethernet/ibm/emac/core.c
++++ b/drivers/net/ethernet/ibm/emac/core.c
+@@ -1161,6 +1161,17 @@ static void emac_clean_rx_ring(struct em
+ 	}
+ }
+ 
++static void emac_clear_mal_desc(struct mal_descriptor *desc, int count)
++{
++	int i;
++
++	for (i = 0; i < count; i++) {
++		desc[i].ctrl = 0;
++		desc[i].data_len = 0;
++		desc[i].data_ptr = 0;
++	}
++}
++
+ static int
+ __emac_prepare_rx_skb(struct sk_buff *skb, struct emac_instance *dev, int slot)
+ {
+@@ -3086,8 +3097,8 @@ static int emac_probe(struct platform_de
+ 	DBG(dev, "rx_desc %p" NL, dev->rx_desc);
+ 
+ 	/* Clean rings */
+-	memset(dev->tx_desc, 0, NUM_TX_BUFF * sizeof(struct mal_descriptor));
+-	memset(dev->rx_desc, 0, NUM_RX_BUFF * sizeof(struct mal_descriptor));
++	emac_clear_mal_desc(dev->tx_desc, NUM_TX_BUFF);
++	emac_clear_mal_desc(dev->rx_desc, NUM_RX_BUFF);
+ 	memset(dev->tx_skb, 0, NUM_TX_BUFF * sizeof(struct sk_buff *));
+ 	memset(dev->rx_skb, 0, NUM_RX_BUFF * sizeof(struct sk_buff *));
+ 

target/linux/apm821xx/patches-6.18/910-dma-direct-Clear-pages-before-coherent-remap.patch

@@ -0,0 +1,72 @@
+From 78bddfc01439de243624b1e60a7f599ec11b55b7 Mon Sep 17 00:00:00 2001
+From: Rosen Penev <rosenp@gmail.com>
+Date: Sat, 16 May 2026 16:08:49 -0700
+Subject: [PATCH] dma-direct: Clear pages before coherent remap
+
+Clear pages through their page mapping before creating a coherent
+remap for dma-direct allocations. Some architectures implement the
+coherent remap as uncached memory, where the generic memset() path may
+use cache-only zeroing instructions that are not valid for the returned
+CPU mapping.
+
+Keep the existing memset() for non-remapped allocations, but avoid
+normal memset() on the remapped coherent allocation path.
+
+Assisted-by: Codex:GPT-5.5
+Signed-off-by: Rosen Penev <rosenp@gmail.com>
+---
+ kernel/dma/direct.c | 20 ++++++++++++++++++--
+ 1 file changed, 18 insertions(+), 2 deletions(-)
+
+--- a/kernel/dma/direct.c
++++ b/kernel/dma/direct.c
+@@ -8,6 +8,7 @@
+ #include <linux/export.h>
+ #include <linux/mm.h>
+ #include <linux/dma-map-ops.h>
++#include <linux/highmem.h>
+ #include <linux/scatterlist.h>
+ #include <linux/pfn.h>
+ #include <linux/vmalloc.h>
+@@ -104,6 +105,15 @@ static void __dma_direct_free_pages(stru
+ 	dma_free_contiguous(dev, page, size);
+ }
+ 
++static void dma_direct_zero_pages(struct page *page, size_t size)
++{
++	unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
++	unsigned long i;
++
++	for (i = 0; i < count; i++)
++		clear_highpage(page + i);
++}
++
+ static struct page *dma_direct_alloc_swiotlb(struct device *dev, size_t size)
+ {
+ 	struct page *page = swiotlb_alloc(dev, size);
+@@ -268,6 +278,13 @@ void *dma_direct_alloc(struct device *de
+ 	if (remap) {
+ 		pgprot_t prot = dma_pgprot(dev, PAGE_KERNEL, attrs);
+ 
++		/*
++		 * Zero via the page mapping before creating a potentially
++		 * uncached remap.  Some architectures cannot safely run normal
++		 * memset on uncached memory.
++		 */
++		dma_direct_zero_pages(page, size);
++
+ 		if (force_dma_unencrypted(dev))
+ 			prot = pgprot_decrypted(prot);
+ 
+@@ -283,10 +300,9 @@ void *dma_direct_alloc(struct device *de
+ 		ret = page_address(page);
+ 		if (dma_set_decrypted(dev, ret, size))
+ 			goto out_leak_pages;
++		memset(ret, 0, size);
+ 	}
+ 
+-	memset(ret, 0, size);
+-
+ 	if (set_uncached) {
+ 		arch_dma_prep_coherent(page, size);
+ 		ret = arch_dma_set_uncached(ret, size);