Re: [PATCH] dmaengine: ste_dma40: turn d40_base phy_chans into a flexible array

[Rosen Penev]

On Wed, May 27, 2026 at 3:14 AM Linus Walleij <linusw@xxxxxxxxxx> wrote:
>
> Hi Rosen,
>
> thanks for your patch!
>
> On Tue, May 26, 2026 at 10:16 PM Rosen Penev <rosenp@xxxxxxxxx> wrote:
>
> > 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).
> >
> > Assisted-by: Claude:Opus-4.7
> > Signed-off-by: Rosen Penev <rosenp@xxxxxxxxx>
>
> OK!
>
> Please add
>
> unsigned int num_phy_chans
>
> > +       struct d40_chan                  phy_chans[];
>
> and
>
> phy_chans[] __counted_by(num_phy_chans);
Not possible here. The allocation allocates space for both phy_chans
and log_chans. To do this I would need to split up allocations into
two. Not a fan of that as two kfrees and two allocs would be needed.
>
>
> > -       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);
>
> Please describe exactly how the ALIGN(sizeof(struct d40_base), 4) requirement
> is met by the new code?
Will do.
>
> The phy_chans will be read by hardware which depends on this specific
> alignment otherwise the data will be corrupted.
>
> Yours,
> Linus Walleij