Re: [PATCHv2 4/4] gpio: Remove VLA from stmpe driver

[Phil Reid]

On 23/03/2018 05:43, Laura Abbott wrote:
> On 03/18/2018 06:29 PM, Phil Reid wrote:
> > On 16/03/2018 02:00, Laura Abbott wrote:
> > > The new challenge is to remove VLAs from the kernel
> > > (see https://lkml.org/lkml/2018/3/7/621)
> > >
> > > This patch replaces a VLA with an appropriate call to kmalloc_array.
> > >
> > > Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
> > > ---
> > > v2: Switch to GFP_KERNEL. There was some discussion about if we should
> > > be doing the allocation at all but given a) the allocation is pretty
> > > small and b) we can possibly take a mutex in a called function I think
> > > this is fine.
> >
> > I still think it's a bad idea. It's simple to preallocate the buffer.
> > But it's up to the maintainer.
>
> I'd feel a lot more confident about doing the global buffer with
> guidance from the maintainer. But looking at the platform data, the
> maximum number of GPIOs is 24, or 3 banks. Maybe we should just always
> stack allocate the maximum since it's fairly small.

That's the other way to go.


> > > ---
> > > Â drivers/gpio/gpio-stmpe.c | 7 ++++++-
> > > Â 1 file changed, 6 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpio/gpio-stmpe.c b/drivers/gpio/gpio-stmpe.c
> > > index f8d7d1cd8488..c2bb20ace6f5 100644
> > > --- a/drivers/gpio/gpio-stmpe.c
> > > +++ b/drivers/gpio/gpio-stmpe.c
> > > @@ -369,10 +369,14 @@ static irqreturn_t stmpe_gpio_irq(int irq, void *dev)
> > > ÂÂÂÂÂ struct stmpe *stmpe = stmpe_gpio->stmpe;
> > > ÂÂÂÂÂ u8 statmsbreg;
> > > ÂÂÂÂÂ int num_banks = DIV_ROUND_UP(stmpe->num_gpios, 8);
> > > -ÂÂÂ u8 status[num_banks];
> > > +ÂÂÂ u8 *status;
> > > ÂÂÂÂÂ int ret;
> > > ÂÂÂÂÂ int i;
> > > +ÂÂÂ status = kmalloc_array(num_banks, sizeof(*status), GFP_KERNEL);
> > > +ÂÂÂ if (!status)
> > > +ÂÂÂÂÂÂÂ return IRQ_NONE;
> > > +
> > > ÂÂÂÂÂ /*
> > > ÂÂÂÂÂÂ * the stmpe_block_read() call below, imposes to set statmsbreg
> > > ÂÂÂÂÂÂ * with the register located at the lowest address. As STMPE1600
> > > @@ -424,6 +428,7 @@ static irqreturn_t stmpe_gpio_irq(int irq, void *dev)
> > > ÂÂÂÂÂÂÂÂÂ }
> > > ÂÂÂÂÂ }
> > > +ÂÂÂ kfree(status);
> > > ÂÂÂÂÂ return IRQ_HANDLED;
> > > Â }


--
Regards
Phil Reid