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Date: Tue, 10 Jul 2012 21:40:05 -0600
From: Bjorn Helgaas <bhelgaas@...gle.com>
To: Jiang Liu <jiang.liu@...wei.com>
Cc: Jiang Liu <liuj97@...il.com>, Don Dutile <ddutile@...hat.com>,
Yinghai Lu <yinghai@...nel.org>,
Taku Izumi <izumi.taku@...fujitsu.com>,
"Rafael J . Wysocki" <rjw@...k.pl>,
Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
Yijing Wang <wangyijing@...wei.com>,
Keping Chen <chenkeping@...wei.com>,
linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [RFC PATCH 05/14] PCI: add access functions for PCIe capabilities
to hide PCIe spec differences
On Tue, Jul 10, 2012 at 9:07 PM, Jiang Liu <jiang.liu@...wei.com> wrote:
> On 2012-7-11 2:35, Bjorn Helgaas wrote:
>>> diff --git a/drivers/pci/access.c b/drivers/pci/access.c
>>> index ba91a7e..80ae022 100644
>>> --- a/drivers/pci/access.c
>>> +++ b/drivers/pci/access.c
>>> @@ -469,3 +469,91 @@ void pci_cfg_access_unlock(struct pci_dev *dev)
>>> raw_spin_unlock_irqrestore(&pci_lock, flags);
>>> }
>>> EXPORT_SYMBOL_GPL(pci_cfg_access_unlock);
>>> +
>>> +static int
>>> +pci_pcie_cap_get_offset(struct pci_dev *dev, int where, size_t sz)
>>> +{
>>> + bool valid;
>>> +
>>> + if (!pci_is_pcie(dev))
>>> + return -EINVAL;
>>> + if (where & (sz - 1))
>>> + return -EINVAL;
>>> +
>>> + if (where < 0)
>>> + valid = false;
>>> + else if (where < PCI_EXP_DEVCAP)
>>> + valid = true;
>>> + else if (where < PCI_EXP_LNKCAP)
>>> + valid = pci_pcie_cap_has_devctl(dev);
>>> + else if (where < PCI_EXP_SLTCAP)
>>> + valid = pci_pcie_cap_has_lnkctl(dev);
>>> + else if (where < PCI_EXP_RTCTL)
>>> + valid = pci_pcie_cap_has_sltctl(dev);
>>> + else if (where < PCI_EXP_DEVCAP2)
>>> + valid = pci_pcie_cap_has_rtctl(dev);
>>> + else if (where < PCI_EXP_CAP2_SIZE)
>>> + valid = pci_pcie_cap_has_cap2(dev);
>>> + else
>>> + valid = false;
>>> +
>>> + return valid ? where + pci_pcie_cap(dev) : -EINVAL;
>>> +}
>>> +
>>> +int pci_pcie_cap_read_word(struct pci_dev *dev, int where, u16 *valp)
>>> +{
>>> + *valp = 0;
>>> + where = pci_pcie_cap_get_offset(dev, where, sizeof(u16));
>>
>> This is a really slick factorization; I like it much better than my
>> proposal. I would like it even *better* if it read something like
>> this:
>>
>> bool implemented;
>>
>> *valp = 0;
>> if (!pci_is_pcie(dev) || where & 1)
>> return -EINVAL;
>>
>> implemented = pci_pcie_cap_implemented(dev, where);
>> if (implemented)
>> return pci_read_config_word(dev, pci_pcie_cap(dev) + where, valp);
>>
>> if (pci_is_pcie(dev) && where == PCI_EXP_SLTSTA ...
>>
>> because I think it's useful to have the "pos + where" visual pattern
>> in the pci_read_config_word() arguments.
> Sure, for better readability.
>
>>
>>> + if (where >= 0)
>>> + return pci_read_config_word(dev, where, valp);
>>> +
>>> + if (pci_is_pcie(dev) && where == PCI_EXP_SLTSTA &&
>>> + pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM)
>>> + *valp = PCI_EXP_SLTSTA_PDS;
>>
>> I think we should be returning success in this case (SLTSTA for
>> downstream port). In fact, I think we should return success even when
>> we're emulating the read of an unimplemented register from a v1
>> capability. The caller should not be aware at all that there is a
>> difference between v1 and v2 capabilities.
>>
>> I'd put the spec reference here rather than in read_dword(), since
>> SLTSTA is a u16 and this is the natural way to read it. Then maybe a
>> short comment in read_dword() below.
> Good point. Return success when reading unimplemented registeres, that
> may simplify code. For we still should return -EINVAL when writing
> unimplemented registers, right?
Yeah, I guess it's OK to return -EINVAL when *writing* to an
unimplemented register. Hopefully the caller is structured such that
we don't even try to write in that case. It'd be interesting to audit
the callers and explore that, but I haven't done that.
>>> +EXPORT_SYMBOL(pci_pcie_cap_write_dword);
>>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>>> index 346b2d9..78767b2 100644
>>> --- a/include/linux/pci.h
>>> +++ b/include/linux/pci.h
>>> @@ -1703,6 +1703,11 @@ static inline bool pci_pcie_cap_has_rtctl(const struct pci_dev *pdev)
>>> type == PCI_EXP_TYPE_RC_EC;
>>> }
>>>
>>> +extern int pci_pcie_cap_read_word(struct pci_dev *dev, int where, u16 *valp);
>>> +extern int pci_pcie_cap_read_dword(struct pci_dev *dev, int where, u32 *valp);
>>> +extern int pci_pcie_cap_write_word(struct pci_dev *dev, int where, u16 val);
>>> +extern int pci_pcie_cap_write_dword(struct pci_dev *dev, int where, u32 val);
>>
>> You don't need the "extern" here (and I think you'll probably remove
>> these altogether, see below).
>>
>>> +
>>> void pci_request_acs(void);
>>> bool pci_acs_enabled(struct pci_dev *pdev, u16 acs_flags);
>>> bool pci_acs_path_enabled(struct pci_dev *start,
>>> @@ -1843,5 +1848,10 @@ static inline struct eeh_dev *pci_dev_to_eeh_dev(struct pci_dev *pdev)
>>> */
>>> struct pci_dev *pci_find_upstream_pcie_bridge(struct pci_dev *pdev);
>>>
>>> +int pci_pcie_capability_read_word(struct pci_dev *dev, int where, u16 *val);
>>> +int pci_pcie_capability_read_dword(struct pci_dev *dev, int where, u32 *val);
>>> +int pci_pcie_capability_write_word(struct pci_dev *dev, int where, u16 val);
>>> +int pci_pcie_capability_write_dword(struct pci_dev *dev, int where, u32 val);
>>
>> There's some confusion here: pci_pcie_cap_* versus
>> pci_pcie_capability_*. I think you only need one set, and I prefer
>> pci_pcie_capability_* to follow the example of
>> pci_bus_find_capability().
> The above confusion was caused by a dirty merge.
>
>>
>>> +
>>> #endif /* __KERNEL__ */
>>> #endif /* LINUX_PCI_H */
>>> diff --git a/include/linux/pci_regs.h b/include/linux/pci_regs.h
>>> index 53274bf..ac60e22 100644
>>> --- a/include/linux/pci_regs.h
>>> +++ b/include/linux/pci_regs.h
>>> @@ -542,9 +542,24 @@
>>> #define PCI_EXP_OBFF_MSGA_EN 0x2000 /* OBFF enable with Message type A */
>>> #define PCI_EXP_OBFF_MSGB_EN 0x4000 /* OBFF enable with Message type B */
>>> #define PCI_EXP_OBFF_WAKE_EN 0x6000 /* OBFF using WAKE# signaling */
>>> -#define PCI_CAP_EXP_ENDPOINT_SIZEOF_V2 44 /* v2 endpoints end here */
>>> +#define PCI_EXP_DEVSTA2 42 /* Device Status 2 */
>>> +#define PCI_CAP_EXP_ENDPOINT_SIZEOF_V2 44 /* v2 endpoints end here */
>>> +#define PCI_EXP_LNKCAP2 44 /* Link Capabilities 2 */
>>> #define PCI_EXP_LNKCTL2 48 /* Link Control 2 */
>>> -#define PCI_EXP_SLTCTL2 56 /* Slot Control 2 */
>>> +#define PCI_EXP_LNKCTL2_TLS 0x0f /* Target Link Speed */
>>> +#define PCI_EXP_LNKCTL2_EC 0x10 /* Enter Compliance */
>>> +#define PCI_EXP_LNKCTL2_HASD 0x20 /* Hardware Autonomous Speed Disable */
>>> +#define PCI_EXP_LNKCTL2_SD 0x40 /* Selectable De-emphasis */
>>> +#define PCI_EXP_LNKCTL2_TM 0x380 /* Transmit Margin */
>>> +#define PCI_EXP_LNKCTL2_EMC 0x400 /* Enter Modified Compliance */
>>> +#define PCI_EXP_LNKCTL2_CS 0x800 /* Compliance SOS */
>>> +#define PCI_EXP_LNKCTL2_CD 0x1000 /* Compliance De-emphasis */
>>> +#define PCI_EXP_LNKSTA2 50 /* Link Status 2 */
>>> +#define PCI_EXP_LNKSTA2_CDL 0x01 /* Current De-emphasis Level */
>>> +#define PCI_EXP_SLTCAP2 52 /* Slot Capabilities 2 */
>>> +#define PCI_EXP_SLTCTL2 56 /* Slot Control 2*/
>>> +#define PCI_EXP_SLTSTA2 58 /* Slot Status 2*/
>>> +#define PCI_EXP_CAP2_SIZE 60
>>
>> Most of these changes look unrelated to the current patch. They
>> should be moved to a patch that uses the symbols you're adding.
> Good point, create on demand:)
>
> Thanks!
> Gerry
>
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