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

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

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.

> 
> dw_pcie_edma_irq_verify() is supposed to verify that nr_irqs is either
> initialized to a valid value by a DWC PCIe glue driver, or that common
> code initializes it.
> 

Yes, but the glue drivers do not set negative value explicitly.

- Mani

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