Re: [PATCH] PCI: dwc: Reject a negative nr_irqs value in dw_pcie_edma_irq_verify()

[Niklas Cassel <cassel@kernel.org>]

On Wed, Jan 01, 2025 at 12:19:13AM +0530, Manivannan Sadhasivam wrote:
> On Tue, Dec 31, 2024 at 07:13:33PM +0100, Niklas Cassel wrote:
> > On Tue, Dec 31, 2024 at 09:21:58PM +0530, Manivannan Sadhasivam wrote:
> > > On Fri, Dec 20, 2024 at 08:23:29AM +0100, Niklas Cassel wrote:
> > > > Platforms that do not have (one or more) dedicated IRQs for the eDMA
> > > > need to set nr_irqs to a non-zero value in their DWC glue driver.
> > > > 
> > > > Platforms that do have (one or more) dedicated IRQs do not need to
> > > > initialize nr_irqs. DWC common code will automatically set nr_irqs.
> > > > 
> > > > Since a glue driver can initialize nr_irqs, dw_pcie_edma_irq_verify()
> > > > should verify that nr_irqs, if non-zero, is a valid value. Thus, add a
> > > > check in dw_pcie_edma_irq_verify() to reject a negative nr_irqs value.
> > > > 
> > > 
> > > Why can't we make dw_edma_chip::nr_irqs unsigned?
> > 
> > dw_edma is defined in drivers/dma/dw-edma/dw-edma-core.h
> > in struct dw_edma.
> > 
> > struct dw_pcie (defined in drivers/pci/controller/dwc/pcie-designware.h)
> > simply has a struct dw_edma as a struct member.
> > 
> > If you bounce on nr_irqs in:
> > drivers/dma/dw-edma/dw-edma-core.c
> > and in
> > drivers/dma/dw-edma/dw-edma-pcie.c
> > you can see that this driver uses signed int for this everywhere.
> > 
> > I didn't feel like refactoring a whole DMA driver.
> > 
> 
> There is no need to refactor. Both 'dma' and 'dwc' drivers do not assume that
> 'nr_irqs' is signed. So simply changing the type to 'unsigned int' is enough.
> I don't see a valid reason to keep it signed and check for negative value.

If you bounce on nr_irqs in
drivers/dma/dw-edma/dw-edma-core.c
and in
drivers/dma/dw-edma/dw-edma-pcie.c

you will see that there are a lot of local variables
that are nr_irqs which are signed, in addition to the
struct member.

I don't want to change the whole driver simply to fix
a warning when building the DWC PCIe driver with W=1.

I have a different solution and will send a V2 soon.


Kind regards,
Niklas