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

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Date:   Wed, 22 Nov 2017 17:24:21 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....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

Hi Lorenzo,

On Wednesday 22 November 2017 05:07 PM, Lorenzo Pieralisi wrote:
> 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

MSI address is written in the MSI capabiltiy register by the host.
> 
> Where is the address set ?
> 
>> 	thinks host supports MSI.
> 
> Add a Fixes: tag please.

sure.
> 
>> 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.

IIUC the host will write to these registers in __pci_write_msi_msg using the
configuration writes.
> 
> 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.

Do you mean dw_pcie_ep_set_msi can overwrite MSI_CAP_MSI_EN and we should avoid
that?

Thanks
Kishon