From: Johan Hovold <johan@kernel.org>
To: Baolin Wang <baolin.wang7@gmail.com>
Cc: Chunyan Zhang <zhang.lyra@gmail.com>,
Johan Hovold <johan@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Orson Zhai <orsonzhai@gmail.com>,
Lee Jones <lee.jones@linaro.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 4/5] mfd: sprd-sc27xx-spi: Fix divide by zero when allocating register offset/mask
Date: Mon, 29 Jun 2020 16:43:25 +0200 [thread overview]
Message-ID: <20200629144325.GV3334@localhost> (raw)
In-Reply-To: <CADBw62r_tkGEr9kHpojAi+fJ+qUqbsc-DQgG1TUAwOdbDXTgNQ@mail.gmail.com>
On Mon, Jun 29, 2020 at 10:35:06PM +0800, Baolin Wang wrote:
> On Mon, Jun 29, 2020 at 10:01 PM Lee Jones <lee.jones@linaro.org> wrote:
> >
> > On Mon, 29 Jun 2020, Johan Hovold wrote:
> >
> > > On Mon, Jun 29, 2020 at 01:32:14PM +0100, Lee Jones wrote:
> > > > Since ddata->irqs[] is already zeroed when allocated by devm_kcalloc() and
> > > > dividing 0 by anything is still 0, there is no need to re-assign
> > > > ddata->irqs[i].* values. Instead, it should be safe to begin at 1.
> > > >
> > > > This fixes the following W=1 warning:
> > > >
> > > > drivers/mfd/sprd-sc27xx-spi.c:255 sprd_pmic_probe() debug: sval_binop_unsigned: divide by zero
> > > >
> > > > Cc: Orson Zhai <orsonzhai@gmail.com>
> > > > Cc: Baolin Wang <baolin.wang7@gmail.com>
> > > > Cc: Chunyan Zhang <zhang.lyra@gmail.com>
> > > > Signed-off-by: Lee Jones <lee.jones@linaro.org>
> > > > ---
> > > > drivers/mfd/sprd-sc27xx-spi.c | 2 +-
> > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/mfd/sprd-sc27xx-spi.c b/drivers/mfd/sprd-sc27xx-spi.c
> > > > index c305e941e435c..694a7d429ccff 100644
> > > > --- a/drivers/mfd/sprd-sc27xx-spi.c
> > > > +++ b/drivers/mfd/sprd-sc27xx-spi.c
> > > > @@ -251,7 +251,7 @@ static int sprd_pmic_probe(struct spi_device *spi)
> > > > return -ENOMEM;
> > > >
> > > > ddata->irq_chip.irqs = ddata->irqs;
> > > > - for (i = 0; i < pdata->num_irqs; i++) {
> > > > + for (i = 1; i < pdata->num_irqs; i++) {
> > > > ddata->irqs[i].reg_offset = i / pdata->num_irqs;
> > > > ddata->irqs[i].mask = BIT(i % pdata->num_irqs);
> > > > }
> > >
> > > This doesn't look right either.
> > >
> > > First, the loop is never executed if num_irqs is zero.
> >
> > The point of the patch is that 0 entries are never processed.
So what's the problem? There's no division by zero here.
And what compiler are you using, Lee? Seems broken.
> > > Second, the current code looks bogus too as reg_offset is always set to
> > > zero and mask to BIT(i)...
>
> Now the result is correct, since all PMIC irq mask bits are in one
> register now, which means the reg_offset is always 0 can work well.
> But I think the logics still can be improved if our PMIC irq numbers
> are larger than 32 in future.
The code is still bogus as pointed out above. Why do you bother to
divide by num_irqs at all?
And what have you guys been smoking? ;)
Johan
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next prev parent reply other threads:[~2020-06-29 14:45 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-29 12:32 [PATCH 0/5] Last batch of W=1 warning fixes in MFD Lee Jones
2020-06-29 12:32 ` [PATCH 1/5] mfd: si476x-cmd: Add missing documentation for si476x_cmd_fm_rds_status()'s arg 'report' Lee Jones
2020-06-29 12:32 ` [PATCH 2/5] mfd: lm3533-ctrlbank: Cap BRIGHTNESS_MAX to 127 since API uses u8 as carrier Lee Jones
2020-06-29 12:51 ` Johan Hovold
2020-06-29 13:25 ` Lee Jones
2020-06-30 8:38 ` Johan Hovold
2020-06-29 12:32 ` [PATCH 3/5] mfd: rave-sp: Fix mistake in 'struct rave_sp_deframer's kerneldoc Lee Jones
2020-06-29 12:32 ` [PATCH 4/5] mfd: sprd-sc27xx-spi: Fix divide by zero when allocating register offset/mask Lee Jones
2020-06-29 13:06 ` Johan Hovold
2020-06-29 14:01 ` Lee Jones
2020-06-29 14:35 ` Baolin Wang
2020-06-29 14:43 ` Johan Hovold [this message]
2020-06-29 15:08 ` Baolin Wang
2020-06-29 15:45 ` Lee Jones
2020-07-01 9:15 ` [PATCH] mfd: sprd-sc27xx-spi: Fix-up bogus IRQ register offset and mask setting Lee Jones
2020-07-01 14:10 ` Baolin Wang
2020-06-29 12:32 ` [PATCH 5/5] mfd: axp20x-i2c: Do not define 'struct acpi_device_id' when !CONFIG_ACPI Lee Jones
2020-06-29 15:38 ` Chen-Yu Tsai
2020-07-06 7:31 ` Lee Jones
2020-07-01 6:59 ` [PATCH v2] mfd: axp20x-i2c: Tell the compiler that ACPI functions may not be used Lee Jones
2020-07-01 8:38 ` Chen-Yu Tsai
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