Re: [PATCH 06/13] PCI: aardvark: Do not clear status bits of masked interrupts

[Marc Zyngier <maz@kernel.org>]

On Tue, 05 Oct 2021 13:13:40 +0100,
Marek Behún <kabel@kernel.org> wrote:
> 
> On Mon, 04 Oct 2021 16:31:54 +0100
> Marc Zyngier <maz@kernel.org> wrote:
> 
> > On Mon, 04 Oct 2021 15:06:53 +0100,
> > Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> wrote:
> > > 
> > > [+Marc - always better to have his eyes on IRQ handling code]
> > > 
> > > On Fri, Oct 01, 2021 at 09:58:49PM +0200, Marek Behún wrote:  
> > > > From: Pali Rohár <pali@kernel.org>
> > > > 
> > > > It is incorrect to clear status bits of masked interrupts.
> > > > 
> > > > The aardvark driver clears all status interrupt bits if no
> > > > unmasked status bit is set. Masked bits should never be cleared.
> > > > 
> > > > Fixes: 8c39d710363c ("PCI: aardvark: Add Aardvark PCI host
> > > > controller driver") Signed-off-by: Pali Rohár <pali@kernel.org>
> > > > Reviewed-by: Marek Behún <kabel@kernel.org>
> > > > Signed-off-by: Marek Behún <kabel@kernel.org>
> > > > Cc: stable@vger.kernel.org
> > > > ---
> > > >  drivers/pci/controller/pci-aardvark.c | 5 +----
> > > >  1 file changed, 1 insertion(+), 4 deletions(-)
> > > > 
> > > > diff --git a/drivers/pci/controller/pci-aardvark.c
> > > > b/drivers/pci/controller/pci-aardvark.c index
> > > > d5d6f92e5143..e4986806a189 100644 ---
> > > > a/drivers/pci/controller/pci-aardvark.c +++
> > > > b/drivers/pci/controller/pci-aardvark.c @@ -1295,11 +1295,8 @@
> > > > static void advk_pcie_handle_int(struct advk_pcie *pcie)
> > > > isr1_mask = advk_readl(pcie, PCIE_ISR1_MASK_REG); isr1_status =
> > > > isr1_val & ((~isr1_mask) & PCIE_ISR1_ALL_MASK); 
> > > > -	if (!isr0_status && !isr1_status) {
> > > > -		advk_writel(pcie, isr0_val, PCIE_ISR0_REG);
> > > > -		advk_writel(pcie, isr1_val, PCIE_ISR1_REG);  
> > > 
> > > This looks fine - on the other hand if no interrupt is set in the
> > > status registers (that are filtered with the masks) we are dealing
> > > with a spurious IRQ right ? Just gauging how severe this is.
> > > 
> > > Lorenzo
> > >   
> > > > +	if (!isr0_status && !isr1_status)
> > > >  		return;  
> > 
> > The whole thing is a bit odd. What the commit message doesn't say is
> > whether the status register shows the status of the line before
> > masking, or after masking.
> 
> I don't quite understand what you are asking about.
> If you are asking about the register itself:
> the PCIE_ISR1_REG says which interrupts are currently set / active,
> including those which are masked.

Then please say so in the commit message.

> If you are asking about the isr1_status variable, it is the
> status of the line after masking. I.e. masked interrupts are not set in
> this variable, only active interrupts which are also unmasked. That is
> obvious from the code.

Which is what I have said... two lines below. If you are going to
reply, please do so in context.

> 
> > The code seems to imply the former, but then the behaviour is
> > awkward. How did we end-up here the first place?
> 
> I answered this in reply to Lorenzo's comment on this patch, see
> https://lore.kernel.org/linux-pci/20211004171823.0288684e@thinkpad/

It did grace my inbox, thanks.

> > if that's only a
> > spurious interrupt, then I'd probably simplify the code altogether,
> > and drop all the early return code. Something like below, as usual
> > completely untested.
> > 
> > 	M.
> > 
> > diff --git a/drivers/pci/controller/pci-aardvark.c
> > b/drivers/pci/controller/pci-aardvark.c index
> > 596ebcfcc82d..1d8f257ecb63 100644 ---
> > a/drivers/pci/controller/pci-aardvark.c +++
> > b/drivers/pci/controller/pci-aardvark.c @@ -1275,7 +1275,8 @@ static
> > void advk_pcie_handle_msi(struct advk_pcie *pcie) static void
> > advk_pcie_handle_int(struct advk_pcie *pcie) {
> >  	u32 isr0_val, isr0_mask, isr0_status;
> > -	u32 isr1_val, isr1_mask, isr1_status;
> > +	u32 isr1_val, isr1_mask;
> > +	unsigned long isr1_status;
> >  	int i;
> >  
> >  	isr0_val = advk_readl(pcie, PCIE_ISR0_REG);
> > @@ -1285,22 +1286,14 @@ static void advk_pcie_handle_int(struct
> > advk_pcie *pcie) isr1_val = advk_readl(pcie, PCIE_ISR1_REG);
> >  	isr1_mask = advk_readl(pcie, PCIE_ISR1_MASK_REG);
> >  	isr1_status = isr1_val & ((~isr1_mask) & PCIE_ISR1_ALL_MASK);
> > -
> > -	if (!isr0_status && !isr1_status) {
> > -		advk_writel(pcie, isr0_val, PCIE_ISR0_REG);
> > -		advk_writel(pcie, isr1_val, PCIE_ISR1_REG);
> > -		return;
> > -	}
> > +	isr1_status >> 8;
> >
> >  	/* Process MSI interrupts */
> >  	if (isr0_status & PCIE_ISR0_MSI_INT_PENDING)
> >  		advk_pcie_handle_msi(pcie);
> >  
> >  	/* Process legacy interrupts */
> > -	for (i = 0; i < PCI_NUM_INTX; i++) {
> > -		if (!(isr1_status & PCIE_ISR1_INTX_ASSERT(i)))
> > -			continue;
> > -
> > +	for_each_set_bit(i, &isr1_status, PCI_NUM_INTX) {
> >  		advk_writel(pcie, PCIE_ISR1_INTX_ASSERT(i),
> >  			    PCIE_ISR1_REG);
> 
> 1. what you are doing here is code cleanup. We are currently in the
>    state where we have lots of fixes for this driver, which we are
>    hoping will go also to stable.

Yes, it is code cleanup. Because I don't find this patch to be very
good, TBH. As for going into stable, that's not relevant for this
discussion.

>    Some of them depend on these changes.
>    Can we please first apply those fixes (we want to send them in
>    batches to avoid sending 60 patchs in one series, since last time
>    nobody wanted to review all of that) and do this afterwards?

It would be better to start with patches that are in a better
shape. After all, this is what the code review process is about. This
isn't "just take my patches".

> 2. you are throwing away lower 8 bits of isr1_status. We have follow-up
>    patches (not in this series, but in another batch which we want to
>    send after this) that will be using those lower 8 bits, so we do not
>    want to throw away them now.

I'm discarding these bits because *in isolation*, that's the correct
thing to do. Feel free to propose a better patch that doesn't discard
these bits and still makes the code more palatable.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.