linux-kernel - Re: [PATCH v2 1/4] skd: Prefer pcie_capability_read

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Date:   Tue, 19 Nov 2019 02:41:45 +0000
From:   Damien Le Moal <Damien.LeMoal@....com>
To:     Frederick Lawler <fred@...dlawl.com>
CC:     "axboe@...nel.dk" <axboe@...nel.dk>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "bvanassche@....org" <bvanassche@....org>
Subject: Re: [PATCH v2 1/4] skd: Prefer pcie_capability_read_word()

On 2019/11/19 10:20, Frederick Lawler wrote:
> Damien Le Moal wrote on 11/17/19 7:45 PM:
>> On 2019/11/18 9:21, Frederick Lawler wrote:
>>> Commit 8c0d3a02c130 ("PCI: Add accessors for PCI Express Capability")
>>> added accessors for the PCI Express Capability so that drivers didn't
>>> need to be aware of differences between v1 and v2 of the PCI
>>> Express Capability.
>>>
>>> Replace pci_read_config_word() and pci_write_config_word() calls with
>>> pcie_capability_read_word() and pcie_capability_write_word().
>>>
>>> Signed-off-by: Frederick Lawler <fred@...dlawl.com>
>>> ---
>>>   drivers/block/skd_main.c | 8 ++------
>>>   1 file changed, 2 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/block/skd_main.c b/drivers/block/skd_main.c
>>> index 51569c199a6c..f25f6ef6b4c7 100644
>>> --- a/drivers/block/skd_main.c
>>> +++ b/drivers/block/skd_main.c
>>> @@ -3134,18 +3134,14 @@ MODULE_DEVICE_TABLE(pci, skd_pci_tbl);
>>>   
>>>   static char *skd_pci_info(struct skd_device *skdev, char *str)
>>>   {
>>> -	int pcie_reg;
>>> -
>>>   	strcpy(str, "PCIe (");
>>> -	pcie_reg = pci_find_capability(skdev->pdev, PCI_CAP_ID_EXP);
>>>   
>>> -	if (pcie_reg) {
>>> +	if (pci_is_pcie(skdev->pdev)) {
>>
>> Maybe return early here ? The reason is that if pci_is_pcie() is false,
>> then the string "PCIe (" is not terminated with a closing parenthesis.
>> So something like:
>>
>> 	if (!pci_is_pcie(skdev->pdev)) {
>> 		strcat(str, ")");
>> 		return str;
>> 	}
>>
>> May be better. Note that the "return str" is also rather pointless since
>> it is not used by the caller of skd_pci_info().
>>
> 
> I agree, but it might be better to include a note that this is not a 
> PCIe device. Reading "PCIe ()" seems weird to me.

Yes indeed. But since this device is PCIe only, if
pci_is_pcie(skdev->pdev) == false, we should probably fail the driver
initialization.

> 
>>>   
>>>   		char lwstr[6];
>>>   		uint16_t pcie_lstat, lspeed, lwidth;
>>>   
>>> -		pcie_reg += 0x12;
>>> -		pci_read_config_word(skdev->pdev, pcie_reg, &pcie_lstat);
>>> +		pcie_capability_read_word(skdev->pdev, 0x12, &pcie_lstat);
>>>   		lspeed = pcie_lstat & (0xF);
>>>   		lwidth = (pcie_lstat & 0x3F0) >> 4;
>>>   
>>>
>>
>>
> 
> Thanks,
> Frederick Lawler
> 
> 


-- 
Damien Le Moal
Western Digital Research