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Wed, 27 May 2026 13:31:44 -0700 (PDT) Received: from ryzen ([2601:644:8000:5b5d:7285:c2ff:fe45:8a32]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2beb56b19f3sm218422455ad.18.2026.05.27.13.31.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 27 May 2026 13:31:43 -0700 (PDT) From: Rosen Penev To: dmaengine@vger.kernel.org Cc: Linus Walleij , Vinod Koul , Frank Li , linux-arm-kernel@lists.infradead.org (moderated list:ARM/NOMADIK/Ux500 ARCHITECTURES), linux-kernel@vger.kernel.org (open list) Subject: [PATCHv2] dmaengine: ste_dma40: turn d40_base phy_chans into a flexible array Date: Wed, 27 May 2026 13:31:26 -0700 Message-ID: <20260527203126.7053-1-rosenp@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: dmaengine@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Convert the separately-offset phy_chans pointer to a C99 flexible array member at the end of struct d40_base, and switch the allocation to struct_size(). The log_chans and memcpy_chans slots continue to live in the same allocation immediately after phy_chans, indexed via base->log_chans. This removes the hand-rolled pointer fixup that recomputed phy_chans from base + ALIGN(sizeof(struct d40_base), 4). The ALIGN(sizeof(struct d40_base), 4) requirement is met implicitly by the C compiler when using a flexible array member. With struct d40_chan phy_chans[] as the last member, the C standard guarantees sizeof(struct d40_base) includes trailing padding to satisfy the alignment of the flexible array element type (struct d40_chan). Since struct d40_chan contains members like spinlock_t, pointers, and struct dma_chan — all with alignment ≥ 4 — the compiler ensures sizeof(struct d40_base) is already a multiple of _Alignof(struct d40_chan) >= 4. The struct_size() macro then computes sizeof(struct d40_base) + sizeof(struct d40_chan) * num_phy_chans, so phy_chans[0] lands at a properly aligned offset without needing the manual ALIGN. Assisted-by: Claude:Opus-4.7 Signed-off-by: Rosen Penev --- v2: added ALIGN description drivers/dma/ste_dma40.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/drivers/dma/ste_dma40.c b/drivers/dma/ste_dma40.c index 9b803c0aec25..d3e3c4cd43f1 100644 --- a/drivers/dma/ste_dma40.c +++ b/drivers/dma/ste_dma40.c @@ -602,7 +602,6 @@ struct d40_base { struct dma_device dma_both; struct dma_device dma_slave; struct dma_device dma_memcpy; - struct d40_chan *phy_chans; struct d40_chan *log_chans; struct d40_chan **lookup_log_chans; struct d40_chan **lookup_phy_chans; @@ -621,6 +620,7 @@ struct d40_base { u32 *regs_interrupt; u16 gcc_pwr_off_mask; struct d40_gen_dmac gen_dmac; + struct d40_chan phy_chans[]; }; static struct device *chan2dev(struct d40_chan *d40c) @@ -3128,6 +3128,7 @@ static int __init d40_hw_detect_init(struct platform_device *pdev, struct clk *clk; void __iomem *virtbase; struct d40_base *base; + size_t alloc_size; int num_log_chans; int num_phy_chans; int num_memcpy_chans; @@ -3197,10 +3198,9 @@ static int __init d40_hw_detect_init(struct platform_device *pdev, "hardware rev: %d with %d physical and %d logical channels\n", rev, num_phy_chans, num_log_chans); - base = devm_kzalloc(dev, - ALIGN(sizeof(struct d40_base), 4) + - (num_phy_chans + num_log_chans + num_memcpy_chans) * - sizeof(struct d40_chan), GFP_KERNEL); + alloc_size = struct_size(base, phy_chans, num_phy_chans); + alloc_size += sizeof(*base->log_chans) * (num_log_chans + num_memcpy_chans); + base = devm_kzalloc(dev, alloc_size, GFP_KERNEL); if (!base) return -ENOMEM; @@ -3213,7 +3213,6 @@ static int __init d40_hw_detect_init(struct platform_device *pdev, base->virtbase = virtbase; base->plat_data = plat_data; base->dev = dev; - base->phy_chans = ((void *)base) + ALIGN(sizeof(struct d40_base), 4); base->log_chans = &base->phy_chans[num_phy_chans]; if (base->plat_data->num_of_phy_chans == 14) { -- 2.54.0