[V5] PCI: loongson: Skip scanning unavailable child devices

  The PCI Controller of 2K1000 could not mask devices by setting vender ID or
device ID in configuration space header as invalid values. When there are
pins shareable between the platform device and the on chip PCI device, if
the platform device is preferred, we should not scan this PCI device. In
the above scene, add `status = "disabled"` property in DT node of this PCI
device.

Before this patch, to solve the above problem, we treat the on chip PCI
devices as platform devices with fixed address assigned by the BIOS. When
there is device not preferred, add the `status = "disabled"` property in DT
node. In kernel, the PCI host bridge only scans slot 9/A/B/C/D/E that are
bridges. Overall, this looks not much elegant.

Signed-off-by: Liu Peibao <liupeibao@loongson.cn>
---
V4 -> V5: make the issue we are facing clear in commit log.
V3 -> V4: 1. get rid of the masklist and search the status property
	  directly.
          2. check the status property only when accessing the vendor ID.
V2 -> V3: 1. use list_for_each_entry() for more clearly.
          2. fix wrong use of sizeof().
V1 -> V2: use existing property "status" instead of adding new property.

 drivers/pci/controller/pci-loongson.c | 11 +++++++++++
 1 file changed, 11 insertions(+)
  

Hi, Peibao,


> -----原始邮件-----
> 发件人: "Liu Peibao" <liupeibao@loongson.cn>
> 发送时间:2022-11-14 15:43:46 (星期一)
> 收件人: "Bjorn Helgaas" <bhelgaas@google.com>, "Rob Herring" <robh+dt@kernel.org>, "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>, "Lorenzo Pieralisi" <lpieralisi@kernel.org>, "Krzysztof Wilczyński" <kw@linux.com>, "Jiaxun Yang" <jiaxun.yang@flygoat.com>, "Christophe JAILLET" <christophe.jaillet@wanadoo.fr>
> 抄送: "Huacai Chen" <chenhuacai@loongson.cn>, "Jianmin Lv" <lvjianmin@loongson.cn>, "Yinbo Zhu" <zhuyinbo@loongson.cn>, wanghongliang <wanghongliang@loongson.cn>, "Liu Peibao" <liupeibao@loongson.cn>, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org
> 主题: [PATCH V5] PCI: loongson: Skip scanning unavailable child devices
> 
> The PCI Controller of 2K1000 could not mask devices by setting vender ID or
I think this patch is needed by both LS2K500 and LS2K1000, so replace 2K1000 with "LS2K" or "Loongson-2K" or "LS2K500/LS2K1000" maybe better. If new version is needed, please change this, thanks.

Huacai

> device ID in configuration space header as invalid values. When there are
> pins shareable between the platform device and the on chip PCI device, if
> the platform device is preferred, we should not scan this PCI device. In
> the above scene, add `status = "disabled"` property in DT node of this PCI
> device.
> 
> Before this patch, to solve the above problem, we treat the on chip PCI
> devices as platform devices with fixed address assigned by the BIOS. When
> there is device not preferred, add the `status = "disabled"` property in DT
> node. In kernel, the PCI host bridge only scans slot 9/A/B/C/D/E that are
> bridges. Overall, this looks not much elegant.
> 
> Signed-off-by: Liu Peibao <liupeibao@loongson.cn>
> ---
> V4 -> V5: make the issue we are facing clear in commit log.
> V3 -> V4: 1. get rid of the masklist and search the status property
> 	  directly.
>           2. check the status property only when accessing the vendor ID.
> V2 -> V3: 1. use list_for_each_entry() for more clearly.
>           2. fix wrong use of sizeof().
> V1 -> V2: use existing property "status" instead of adding new property.
> 
>  drivers/pci/controller/pci-loongson.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/pci/controller/pci-loongson.c b/drivers/pci/controller/pci-loongson.c
> index 05c50408f13b..efca0b3b5a29 100644
> --- a/drivers/pci/controller/pci-loongson.c
> +++ b/drivers/pci/controller/pci-loongson.c
> @@ -194,6 +194,17 @@ static void __iomem *pci_loongson_map_bus(struct pci_bus *bus,
>  			return NULL;
>  	}
>  
> +#ifdef CONFIG_OF
> +	/* Don't access disabled devices. */
> +	if (pci_is_root_bus(bus) && where == PCI_VENDOR_ID) {
> +		struct device_node *dn;
> +
> +		dn = of_pci_find_child_device(bus->dev.of_node, devfn);
> +		if (dn && !of_device_is_available(dn))
> +			return NULL;
> +	}
> +#endif
> +
>  	/* CFG0 can only access standard space */
>  	if (where < PCI_CFG_SPACE_SIZE && priv->cfg0_base)
>  		return cfg0_map(priv, bus, devfn, where);
> -- 
> 2.20.1


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On 11/14/22 4:14 PM, 陈华才 wrote:
> Hi, Peibao,
> 
> 
>> -----原始邮件-----
>> 发件人: "Liu Peibao" <liupeibao@loongson.cn>
>> 发送时间:2022-11-14 15:43:46 (星期一)
>> 收件人: "Bjorn Helgaas" <bhelgaas@google.com>, "Rob Herring" <robh+dt@kernel.org>, "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>, "Lorenzo Pieralisi" <lpieralisi@kernel.org>, "Krzysztof Wilczyński" <kw@linux.com>, "Jiaxun Yang" <jiaxun.yang@flygoat.com>, "Christophe JAILLET" <christophe.jaillet@wanadoo.fr>
>> 抄送: "Huacai Chen" <chenhuacai@loongson.cn>, "Jianmin Lv" <lvjianmin@loongson.cn>, "Yinbo Zhu" <zhuyinbo@loongson.cn>, wanghongliang <wanghongliang@loongson.cn>, "Liu Peibao" <liupeibao@loongson.cn>, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org
>> 主题: [PATCH V5] PCI: loongson: Skip scanning unavailable child devices
>>
>> The PCI Controller of 2K1000 could not mask devices by setting vender ID or
> I think this patch is needed by both LS2K500 and LS2K1000, so replace 2K1000 with "LS2K" or "Loongson-2K" or "LS2K500/LS2K1000" maybe better. If new version is needed, please change this, thanks.
> 

LS2K500 does not need this as there are no on chip PCI devices.

BR,
Peibao
  

Hi Liu,

On Mon, Nov 14, 2022 at 03:43:46PM +0800, Liu Peibao wrote:
> The PCI Controller of 2K1000 could not mask devices by setting vender ID or
> device ID in configuration space header as invalid values.

I don't think this 2K1000 information is really relevant.  I
understand that some chipsets might support this, and they might use
that to avoid this issue, but there's no PCI requirement that the
Vendor/Device ID be writable by anything.

> When there are
> pins shareable between the platform device and the on chip PCI device, if

What does "pins shareable between the platform device and the on chip
PCI device" mean?

I assume there's a single device in the hardware, and both the
"platform device" and the PCI device" refer to that single device?

And there's some reason you prefer to use the platform device
interface to enumerate that device?

> the platform device is preferred, we should not scan this PCI device. In
> the above scene, add `status = "disabled"` property in DT node of this PCI
> device.
> 
> Before this patch, to solve the above problem, we treat the on chip PCI
> devices as platform devices with fixed address assigned by the BIOS.

This says "before this patch".  But the rest of the sentence sounds
like what happens *after* this patch.

> When
> there is device not preferred, add the `status = "disabled"` property in DT
> node.

> In kernel, the PCI host bridge only scans slot 9/A/B/C/D/E that are
> bridges.

I guess this has something to do with pdev_may_exist() [1], but why do
you mention it here?  Do you intend to remove pdev_may_exist() and use
this DT mechanism instead?

Bjorn

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/controller/pci-loongson.c?id=v6.0#n168

> Overall, this looks not much elegant.
> 
> Signed-off-by: Liu Peibao <liupeibao@loongson.cn>
> ---
> V4 -> V5: make the issue we are facing clear in commit log.
> V3 -> V4: 1. get rid of the masklist and search the status property
> 	  directly.
>           2. check the status property only when accessing the vendor ID.
> V2 -> V3: 1. use list_for_each_entry() for more clearly.
>           2. fix wrong use of sizeof().
> V1 -> V2: use existing property "status" instead of adding new property.
> 
>  drivers/pci/controller/pci-loongson.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/pci/controller/pci-loongson.c b/drivers/pci/controller/pci-loongson.c
> index 05c50408f13b..efca0b3b5a29 100644
> --- a/drivers/pci/controller/pci-loongson.c
> +++ b/drivers/pci/controller/pci-loongson.c
> @@ -194,6 +194,17 @@ static void __iomem *pci_loongson_map_bus(struct pci_bus *bus,
>  			return NULL;
>  	}
>  
> +#ifdef CONFIG_OF
> +	/* Don't access disabled devices. */
> +	if (pci_is_root_bus(bus) && where == PCI_VENDOR_ID) {
> +		struct device_node *dn;
> +
> +		dn = of_pci_find_child_device(bus->dev.of_node, devfn);
> +		if (dn && !of_device_is_available(dn))
> +			return NULL;
> +	}
> +#endif
> +
>  	/* CFG0 can only access standard space */
>  	if (where < PCI_CFG_SPACE_SIZE && priv->cfg0_base)
>  		return cfg0_map(priv, bus, devfn, where);
> -- 
> 2.20.1
>
  

On 11/15/22 1:11 AM, Bjorn Helgaas wrote:
> Hi Liu,
> 
> On Mon, Nov 14, 2022 at 03:43:46PM +0800, Liu Peibao wrote:
>> The PCI Controller of 2K1000 could not mask devices by setting vender ID or
>> device ID in configuration space header as invalid values.
> 
> I don't think this 2K1000 information is really relevant.  I
> understand that some chipsets might support this, and they might use
> that to avoid this issue, but there's no PCI requirement that the
> Vendor/Device ID be writable by anything.
> 

OK, I think I got it.

>> When there are
>> pins shareable between the platform device and the on chip PCI device, if
> 
> What does "pins shareable between the platform device and the on chip
> PCI device" mean?
> 
> I assume there's a single device in the hardware, and both the
> "platform device" and the PCI device" refer to that single device?
> 
> And there's some reason you prefer to use the platform device
> interface to enumerate that device?
> 

No, they are not the same device. For example, GMAC1(on chip PCI device) and
GPIO(platform device, not PCI device) 14 use the same pin. The function for
this pin can be configured by one bit in general register, eg, 0 for GPIO 14,
1 for GMAC1. Sometimes, GPIO 14 is preferred, so configure the pin with
function GPIO 14 and disable GMAC1.

>> the platform device is preferred, we should not scan this PCI device. In
>> the above scene, add `status = "disabled"` property in DT node of this PCI
>> device.
>>
>> Before this patch, to solve the above problem, we treat the on chip PCI
>> devices as platform devices with fixed address assigned by the BIOS.
> 
> This says "before this patch".  But the rest of the sentence sounds
> like what happens *after* this patch.
> 

In fact, I want to describe an solution. But it seems that I described a
little confusing and please check the refactored commit log in the
following comments.

>> When
>> there is device not preferred, add the `status = "disabled"` property in DT
>> node.
> 
>> In kernel, the PCI host bridge only scans slot 9/A/B/C/D/E that are
>> bridges.
> 
> I guess this has something to do with pdev_may_exist() [1], but why do
> you mention it here?  Do you intend to remove pdev_may_exist() and use
> this DT mechanism instead?
> 
> Bjorn
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/controller/pci-loongson.c?id=v6.0#n168
> 

You are right and I did something ugly in pdev_may_exist() in my kernel. I
really don't want to continue doing this, so I am developing this patch.

Also I don't want to remove pdev_may_exist(). This patch could replace
pdev_may_exist() only in DT, but pdev_may_exist() matters in both ACPI and DT.

Overall, how about the following refactored commit log:

"This patch adds a mechanism to disable on chip PCI devices by DT. Typically,
when there are pins shareable between the platform device and the on chip PCI
device, if the PCI device is not preferred, add `status = "disabled"` property
to this PCI device DT node.

For example, on LS2K1000, GMAC1(on chip PCI device) and GPIO(platform device,
not PCI device) 14 share the same pin. If GMAC1 is not preferred, add
`status = "disabled"` property in GMAC1 DT node."

BR,
Peibao
  

On Wed, Nov 16, 2022 at 05:57:46PM +0800, Liu Peibao wrote:
> On 11/15/22 1:11 AM, Bjorn Helgaas wrote:
> > On Mon, Nov 14, 2022 at 03:43:46PM +0800, Liu Peibao wrote:

> > I assume there's a single device in the hardware, and both the
> > "platform device" and the PCI device" refer to that single device?
> > 
> > And there's some reason you prefer to use the platform device
> > interface to enumerate that device?
> 
> No, they are not the same device. For example, GMAC1(on chip PCI device) and
> GPIO(platform device, not PCI device) 14 use the same pin. The function for
> this pin can be configured by one bit in general register, eg, 0 for GPIO 14,
> 1 for GMAC1. Sometimes, GPIO 14 is preferred, so configure the pin with
> function GPIO 14 and disable GMAC1.

Ah, I see, so there's some circuit that can be driven by either the
platform (GPIO) device or the PCI (GMAC1) device.

> Overall, how about the following refactored commit log:
> 
> "This patch adds a mechanism to disable on chip PCI devices by DT. Typically,
> when there are pins shareable between the platform device and the on chip PCI
> device, if the PCI device is not preferred, add `status = "disabled"` property
> to this PCI device DT node.
> 
> For example, on LS2K1000, GMAC1(on chip PCI device) and GPIO(platform device,
> not PCI device) 14 share the same pin. If GMAC1 is not preferred, add
> `status = "disabled"` property in GMAC1 DT node."

  Add a mechanism ...

(Instead of "This patch adds ..."; no need to say "this patch" because
it's obvious that the commit log applies to *this patch*)

Add spaces before "(", e.g., "GMAC1 (on-chip PCI device)".

Looks good!

Bjorn
  

On 11/17/22 2:14 AM, Bjorn Helgaas wrote:
> On Wed, Nov 16, 2022 at 05:57:46PM +0800, Liu Peibao wrote:
>> On 11/15/22 1:11 AM, Bjorn Helgaas wrote:
>>> On Mon, Nov 14, 2022 at 03:43:46PM +0800, Liu Peibao wrote:
> 
>>> I assume there's a single device in the hardware, and both the
>>> "platform device" and the PCI device" refer to that single device?
>>>
>>> And there's some reason you prefer to use the platform device
>>> interface to enumerate that device?
>>
>> No, they are not the same device. For example, GMAC1(on chip PCI device) and
>> GPIO(platform device, not PCI device) 14 use the same pin. The function for
>> this pin can be configured by one bit in general register, eg, 0 for GPIO 14,
>> 1 for GMAC1. Sometimes, GPIO 14 is preferred, so configure the pin with
>> function GPIO 14 and disable GMAC1.
> 
> Ah, I see, so there's some circuit that can be driven by either the
> platform (GPIO) device or the PCI (GMAC1) device.
> 

That is really the point. Sorry for my poor description and English :).

>> Overall, how about the following refactored commit log:
>>
>> "This patch adds a mechanism to disable on chip PCI devices by DT. Typically,
>> when there are pins shareable between the platform device and the on chip PCI
>> device, if the PCI device is not preferred, add `status = "disabled"` property
>> to this PCI device DT node.
>>
>> For example, on LS2K1000, GMAC1(on chip PCI device) and GPIO(platform device,
>> not PCI device) 14 share the same pin. If GMAC1 is not preferred, add
>> `status = "disabled"` property in GMAC1 DT node."
> 
>   Add a mechanism ...
> 
> (Instead of "This patch adds ..."; no need to say "this patch" because
> it's obvious that the commit log applies to *this patch*)
> 
> Add spaces before "(", e.g., "GMAC1 (on-chip PCI device)".
> 
> Looks good!
> 
> Bjorn
> 

I will modify these and send the next version patch.

Thanks a lot!

BR,
Peibao