[PATCH] PCI: rockchip: check link status when validating device

[Shawn Lin]

Hi Bjorn,

在 2017/5/24 3:44, Bjorn Helgaas 写道:
> On Fri, May 19, 2017 at 02:58:27PM +0800, Shawn Lin wrote:
>> This patch checks the link status before reading and
>> writing configure space of devices attached to the RC.
>> If the link status is down, we shouldn't try to access
>> the devices.
>
> What bad things happen without this patch?
>
> It's racy to check the link status, then do the config access.  The
> link might go down after we check but before we can perform the
> access.

yes, it cannot fix the issue cleanly. Also we cannot prevent
the access from memory read/write that doesn't call the
pci_read/write_config_foo APIs.

I just thought we could catch one luckly before performing
configure access.

>
>> Signed-off-by: Shawn Lin <shawn.lin at rock-chips.com>
>> ---
>>
>>  drivers/pci/host/pcie-rockchip.c | 12 ++++++++++++
>>  1 file changed, 12 insertions(+)
>>
>> diff --git a/drivers/pci/host/pcie-rockchip.c b/drivers/pci/host/pcie-rockchip.c
>> index 0e020b6..1e64227 100644
>> --- a/drivers/pci/host/pcie-rockchip.c
>> +++ b/drivers/pci/host/pcie-rockchip.c
>> @@ -275,9 +275,21 @@ static void rockchip_pcie_update_txcredit_mui(struct rockchip_pcie *rockchip)
>>  	rockchip_pcie_write(rockchip, val, PCIE_CORE_TXCREDIT_CFG1);
>>  }
>>
>> +static inline bool rockchip_pcie_link_up(struct rockchip_pcie *rockchip)
>> +{
>> +	return PCIE_LINK_UP(rockchip_pcie_read(rockchip,
>> +					PCIE_CLIENT_BASIC_STATUS1));
>> +}
>> +
>>  static int rockchip_pcie_valid_device(struct rockchip_pcie *rockchip,
>>  				      struct pci_bus *bus, int dev)
>>  {
>> +	/* do not access the devices if the link isn't completed */
>> +	if (bus->number != rockchip->root_bus_nr) {
>> +		if (!rockchip_pcie_link_up(rockchip))
>> +			return 0;
>> +	}
>> +
>>  	/* access only one slot on each root port */
>>  	if (bus->number == rockchip->root_bus_nr && dev > 0)
>>  		return 0;
>> --
>> 1.9.1
>>
>>
>
>
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