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Mon, 6 Jul 2026 08:27:11 +0000 (GMT) From: Nikhil Kumar Singh To: linuxppc-dev@lists.ozlabs.org, mkchauras@gmail.com Cc: linux-kernel@vger.kernel.org, maddy@linux.ibm.com, mpe@ellerman.id.au, npiggin@gmail.com, chleroy@kernel.org, adityag@linux.ibm.com, mahesh@linux.ibm.com, Nikhil Kumar Singh Subject: [PATCH v2] powerpc/64s: Clarify copy_and_flush() cache sync loop comment Date: Mon, 6 Jul 2026 13:57:08 +0530 Message-ID: <20260706082708.43918-1-nikhilks@linux.ibm.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260701182756.273019-1-nikhilks@linux.ibm.com> References: <20260701182756.273019-1-nikhilks@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: zt5-GowiQNmNqbXcpvdrLMACwdKr0kee X-Proofpoint-Spam-Info: AW1haW4tMjYwNzA2MDA4MyBTYWx0ZWRfXw6P6/sdf4SPM OIe37qPDx+zDfSL4k/whmmIjW+0ekgd40Ear/BGEHZdFs/xjzvCv1e2S/XC/onM81do3YObDMme lO4sNx0089dHSeZqbui9hQREbf0BFao= X-Authority-Analysis: v=2.4 cv=DKW/JSNb c=1 sm=1 tr=0 ts=6a4b66e6 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VnNF1IyMAAAA:8 a=EMOAY_goFwyYI0LnCuEA:9 X-Proofpoint-GUID: ZniIbTu-OUuwlMyHTG6AXcOW3Rs5DHYc X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzA2MDA4MyBTYWx0ZWRfX5vhcNPrNU9O6 s5oATm3xCVq/ewAeJFTpuZFv680Y+HA1hfDt+7lop8O9wJCiYzq5GEX/KXtRcA08nIvWt3EQ7yb xkamnsnKJfPAb+D/jMKvIv7XiFTo8//XtwJiJFNHPmgGKM9JAdrqxyHXnYGB2OXC2vLLFpaf7Wg HWEzzqgUV+tNTFWN6plhGhE9NRyQ2HLxAoejT4cCtb2IK0pzmXfrQP0R1ECC71OLv1zweg3sXzr y4plPAHbyuxQYzYwKAj8KUt2B69MLmShw+kxBAFGveK22WEyQLHY4qv52rrTrrcbmpGMZQd11n9 HJOA1rYLMUrR8wz20wqKGqujTkrzG7dH6vT8Kk06MEsyJIf/CH84diu7H/IB8ae1O3xyp6pF31L 9WUGNIFsKNp96DRArNibMqiDQkW7PC4TB4uEIjzDNuRVzXSLmhc9m7/NtEyGBg2UEXPNwj9Err+ /oZMfmcA6m65Q8mva9w== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-07-05_02,2026-07-03_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 bulkscore=0 clxscore=1015 phishscore=0 impostorscore=0 priorityscore=1501 adultscore=0 lowpriorityscore=0 suspectscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607060083 The value loaded into r0 in copy_and_flush() represents the number of 8-byte words processed between cache synchronization operations. The existing comment refers to cache line size, which can make it appear that the value is a cache line size in bytes rather than a loop count. Clarify the comment to explain that the loop processes 8 words (64 bytes) per cache synchronization iteration, and that increasing the value would skip cache maintenance for intermediate cache lines. This is a comment-only change with no functional impact. Signed-off-by: Nikhil Kumar Singh --- arch/powerpc/kernel/head_64.S | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-) diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S index 63432a33ec49..a54f6f979173 100644 --- a/arch/powerpc/kernel/head_64.S +++ b/arch/powerpc/kernel/head_64.S @@ -713,14 +713,18 @@ p_end: .8byte _end - copy_to_here _GLOBAL(copy_and_flush) addi r5,r5,-8 addi r6,r6,-8 -4: li r0,8 /* Use the smallest common */ - /* denominator cache line */ - /* size. This results in */ - /* extra cache line flushes */ - /* but operation is correct. */ - /* Can't get cache line size */ - /* from NACA as it is being */ - /* moved too. */ +4: li r0,8 /* r0 is the number of 8-byte words */ + /* to copy per cache sync iteration. */ + /* 8 words * 8 bytes = 64 bytes. 64B is */ + /* the current default cache line size. */ + /* This is a loop count, not a byte */ + /* count. Increasing it may skip */ + /* dcbst/icbi for lines in between and */ + /* leave stale instructions in icache. */ + /* This results in extra cache line */ + /* flushes but operation is correct. */ + /* Can't get cache line size from NACA */ + /* as it is being moved too. */ mtctr r0 /* put # words/line in ctr */ 3: addi r6,r6,8 /* copy a cache line */ -- 2.43.5