dmaengine: ste_dma40: turn d40_base phy_chans into a flexible array

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>

diff --git a/drivers/dma/ste_dma40.c b/drivers/dma/ste_dma40.c
index 9b803c0aec25419f7a4c330c8d14be89f043b1b0..0d9ffa3e266398187dc4ab92dab72f477b97cea1 100644 (file)
--- 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 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) {