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Sat, 30 May 2026 19:09:01 -0700 (PDT) Received: from ryzen ([2601:644:8000:5b5d:7285:c2ff:fe45:8a32]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8ccea042229sm57814566d6.5.2026.05.30.19.08.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 30 May 2026 19:09:00 -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: [PATCHv3] dmaengine: ste_dma40: turn d40_base phy_chans into a flexible array Date: Sat, 30 May 2026 19:08:43 -0700 Message-ID: <20260531020843.594892-1-rosenp@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable 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 =E2=80=94 a= ll with alignment =E2=89=A5 4 =E2=80=94 the compiler ensures sizeof(struct d40_base= ) is already a multiple of _Alignof(struct d40_chan) >=3D 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 manu= al ALIGN. Assisted-by: Claude:Opus-4.7 Signed-off-by: Rosen Penev Reviewed-by: Linus Walleij --- v3: add min() calls v2: added ALIGN description drivers/dma/ste_dma40.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/drivers/dma/ste_dma40.c b/drivers/dma/ste_dma40.c index 9b803c0aec25..0d9ffa3e2663 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; @@ -3185,22 +3186,24 @@ static int __init d40_hw_detect_init(struct platfor= m_device *pdev, else num_phy_chans =3D 4 * (readl(virtbase + D40_DREG_ICFG) & 0x7) + 4; + num_phy_chans =3D min(num_phy_chans, STEDMA40_MAX_PHYS); + /* The number of channels used for memcpy */ if (plat_data->num_of_memcpy_chans) num_memcpy_chans =3D plat_data->num_of_memcpy_chans; else num_memcpy_chans =3D ARRAY_SIZE(dma40_memcpy_channels); + num_memcpy_chans =3D min(num_memcpy_chans, D40_MEMCPY_MAX_CHANS); num_log_chans =3D num_phy_chans * D40_MAX_LOG_CHAN_PER_PHY; dev_info(dev, "hardware rev: %d with %d physical and %d logical channels\n", rev, num_phy_chans, num_log_chans); - base =3D 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 =3D struct_size(base, phy_chans, num_phy_chans); + alloc_size +=3D sizeof(*base->log_chans) * (num_log_chans + num_memcpy_ch= ans); + base =3D devm_kzalloc(dev, alloc_size, GFP_KERNEL); if (!base) return -ENOMEM; @@ -3213,7 +3216,6 @@ static int __init d40_hw_detect_init(struct platform_= device *pdev, base->virtbase =3D virtbase; base->plat_data =3D plat_data; base->dev =3D dev; - base->phy_chans =3D ((void *)base) + ALIGN(sizeof(struct d40_base), 4); base->log_chans =3D &base->phy_chans[num_phy_chans]; if (base->plat_data->num_of_phy_chans =3D=3D 14) { -- 2.54.0