linux-kernel - Re: [PATCH] PCI: designware-ep: Fix ->get_msi() to check MSI

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Date:   Wed, 22 Nov 2017 11:37:49 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Kishon Vijay Abraham I <kishon@...com>
Cc:     Jingoo Han <jingoohan1@...il.com>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, nsekhar@...com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xiaowei Bao <xiaowei.bao@....com>,
        Niklas Cassel <niklas.cassel@...s.com>
Subject: Re: [PATCH] PCI: designware-ep: Fix ->get_msi() to check MSI_EN bit

On Wed, Nov 22, 2017 at 02:34:27PM +0530, Kishon Vijay Abraham I wrote:
> ->get_msi() now checks MSI_EN bit in the MSI CAPABILITY register to
> find whether the host supports MSI instead of using the
> MSI ADDRESS in the MSI CAPABILITY register.

I think that's a sensible thing to do regardless, given that I do not
understand why 0x0 can't be a valid MSI address in the first place.

> This fixes the issue with the following sequence
>   'modprobe pci_endpoint_test' enables MSI
>   'rmmod pci_endpoint_test' disables MSI but MSI address has a valid value
>   'modprobe pci_endpoint_test no_msi=1' - Since MSI address has a valid
> 	value (set during the previous insertion of the module), EP

Where is the address set ?

> 	thinks host supports MSI.

Add a Fixes: tag please.

> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
> ---
>  drivers/pci/dwc/pcie-designware-ep.c | 12 +++---------
>  drivers/pci/dwc/pcie-designware.h    |  1 +
>  2 files changed, 4 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/pci/dwc/pcie-designware-ep.c b/drivers/pci/dwc/pcie-designware-ep.c
> index d53d5f168363..7c621877a939 100644
> --- a/drivers/pci/dwc/pcie-designware-ep.c
> +++ b/drivers/pci/dwc/pcie-designware-ep.c
> @@ -197,20 +197,14 @@ static int dw_pcie_ep_map_addr(struct pci_epc *epc, phys_addr_t addr,
>  static int dw_pcie_ep_get_msi(struct pci_epc *epc)
>  {
>  	int val;
> -	u32 lower_addr;
> -	u32 upper_addr;
>  	struct dw_pcie_ep *ep = epc_get_drvdata(epc);
>  	struct dw_pcie *pci = to_dw_pcie_from_ep(ep);
>  
> -	val = dw_pcie_readb_dbi(pci, MSI_MESSAGE_CONTROL);
> -	val = (val & MSI_CAP_MME_MASK) >> MSI_CAP_MME_SHIFT;
> -
> -	lower_addr = dw_pcie_readl_dbi(pci, MSI_MESSAGE_ADDR_L32);
> -	upper_addr = dw_pcie_readl_dbi(pci, MSI_MESSAGE_ADDR_U32);

I can't find code that writes these registers, see above for my
question.

On top of that I think that what's done the EPF test function driver in
struct pci_epf.bind() should be undone in struct pci_epf.unbind() and I
do not think that's happening for MSIs.

> -
> -	if (!(lower_addr || upper_addr))
> +	val = dw_pcie_readw_dbi(pci, MSI_MESSAGE_CONTROL);

MSI_MESSAGE_CONTROL is written in dw_pcie_ep_set_msi(), I assume a write
to bit[0] (ie MSI_CAP_MSI_EN_MASK) is ignored - it would be good if you
can clarify that as well please.

Thanks,
Lorenzo

> +	if (!(val & MSI_CAP_MSI_EN_MASK))
>  		return -EINVAL;
>  
> +	val = (val & MSI_CAP_MME_MASK) >> MSI_CAP_MME_SHIFT;
>  	return val;
>  }
>  
> diff --git a/drivers/pci/dwc/pcie-designware.h b/drivers/pci/dwc/pcie-designware.h
> index e5d9d77b778e..cb493bcae8b4 100644
> --- a/drivers/pci/dwc/pcie-designware.h
> +++ b/drivers/pci/dwc/pcie-designware.h
> @@ -101,6 +101,7 @@
>  #define MSI_MESSAGE_CONTROL		0x52
>  #define MSI_CAP_MMC_SHIFT		1
>  #define MSI_CAP_MME_SHIFT		4
> +#define MSI_CAP_MSI_EN_MASK		0x1
>  #define MSI_CAP_MME_MASK		(7 << MSI_CAP_MME_SHIFT)
>  #define MSI_MESSAGE_ADDR_L32		0x54
>  #define MSI_MESSAGE_ADDR_U32		0x58
> -- 
> 2.11.0
>