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dmaengine: ste_dma40: turn d40_base phy_chans into a flexible array

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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 <rosenp@gmail.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Link: https://patch.msgid.link/20260531020843.594892-1-rosenp@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
This commit is contained in:
Rosen Penev 2026-05-30 19:08:43 -07:00 committed by Vinod Koul
parent b55bfcc677
commit cc4fea19da
1 changed files with 8 additions and 6 deletions
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14
drivers/dma/ste_dma40.c
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@ -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 platform_device *pdev,
else
num_phy_chans = 4 * (readl(virtbase + D40_DREG_ICFG) & 0x7) + 4;
num_phy_chans = min(num_phy_chans, STEDMA40_MAX_PHYS);
/* The number of channels used for memcpy */
if (plat_data->num_of_memcpy_chans)
num_memcpy_chans = plat_data->num_of_memcpy_chans;
else
num_memcpy_chans = ARRAY_SIZE(dma40_memcpy_channels);
num_memcpy_chans = min(num_memcpy_chans, D40_MEMCPY_MAX_CHANS);
num_log_chans = 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 = 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 +3216,6 @@ 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) {