Re: [PATCH V2] PCI: tegra: Fix building Tegra194 PCIe driver

[Jon Hunter <jonathanh@nvidia.com>]

On 20/05/2021 23:19, Bjorn Helgaas wrote:
> On Thu, May 20, 2021 at 10:01:23AM +0100, Jon Hunter wrote:
>> Commit 7f100744749e ("PCI: tegra: Add Tegra194 MCFG quirks for ECAM
>> errata") caused a few build regressions for the Tegra194 PCIe driver
>> which are:
>>
>> 1. The Tegra194 PCIe driver can no longer be built as a module. This
>>    was caused by removing the Makefile entry to build the pcie-tegra.c
>>    based upon the CONFIG_PCIE_TEGRA194 option. Therefore, restore this
>>    so that we can build the driver as a module if ACPI support is not
>>    enabled in the kernel.
> 
> I'm not sure what "if ACPI support is not enabled in the kernel" is
> telling me.  Does it mean that we can only build tegra194 as a module
> if ACPI is not enabled?  I don't think so (at least, I don't think
> Kconfig enforces that).

If ACPI is enabled, then we will build the driver into the kernel. If we
have ...

 CONFIG_ACPI=y
 CONFIG_PCIE_TEGRA194=m

FWICS the pcie-tegra194.c driver is builtin to the kernel.
	> Should the "if ACPI support is not enabled ..." part just be dropped?
> 
> I assume it should be possible to build the kernel with ACPI enabled
> and with pcie-tegra194 as a module?

Per the above that does not appear to be possible.

>> 2. If CONFIG_PCIE_TEGRA194 is configured to build the driver as a
>>    module, at the same time that CONFIG_ACPI and CONFIG_PCI_QUIRKS are
>>    selected to build the driver into the kernel, then the necessary
>>    functions in the driver to probe and remove the device when booting
>>    with device-tree and not compiled into to the driver. This prevents
>>    the PCIe devices being probed when booting with device-tree. Fix this
>>    by using the IS_ENABLED() macro.
> 
> The #ifdef vs IS_ENABLED() difference is kind of subtle and I have to
> figure it out every time.  Maybe something like this?
> 
>   7f100744749e ("PCI: tegra: Add Tegra194 MCFG quirks for ECAM
>   errata") added "#ifdef CONFIG_PCIE_TEGRA194" around the native
>   driver.
> 
>   But if we set CONFIG_PCIE_TEGRA194=m to build the driver as a
>   module, autoconf.h contains "#define CONFIG_PCIE_TEGRA194_MODULE 1"
>   (not "#define CONFIG_PCIE_TEGRA194 1"), so the #ifdef excludes the
>   driver.
> 
>   Instead, use "IS_ENABLED(CONFIG_PCIE_TEGRA194)", which checks for
>   either CONFIG_PCIE_TEGRA194 or CONFIG_PCIE_TEGRA194_MODULE.

OK sounds good. Thanks

>> 3. The below build warnings to be seen with particular kernel
>>    configurations. Fix these by adding the necessary guards around these
>>    variable definitions.
>>
>>   drivers/pci/controller/dwc/pcie-tegra194.c:259:18: warning:
>>   	‘event_cntr_data_offset’ defined but not used [-Wunused-const-variable=]
>>   drivers/pci/controller/dwc/pcie-tegra194.c:250:18: warning:
>>   	‘event_cntr_ctrl_offset’ defined but not used [-Wunused-const-variable=]
>>   drivers/pci/controller/dwc/pcie-tegra194.c:243:27: warning:
>>   	‘pcie_gen_freq’ defined but not used [-Wunused-const-variable=]
>>
>> Fixes: 7f100744749e ("PCI: tegra: Add Tegra194 MCFG quirks for ECAM errata")
>> Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
> 
> This is a candidate for v5.13, since we merged 7f100744749e for
> v5.13-rc1.

Yes we need to fix for v5.13.

>> ---
>>  drivers/pci/controller/dwc/Makefile        | 1 +
>>  drivers/pci/controller/dwc/pcie-tegra194.c | 6 +++++-
>>  2 files changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/controller/dwc/Makefile b/drivers/pci/controller/dwc/Makefile
>> index eca805c1a023..f0d1e2d8c022 100644
>> --- a/drivers/pci/controller/dwc/Makefile
>> +++ b/drivers/pci/controller/dwc/Makefile
>> @@ -32,6 +32,7 @@ obj-$(CONFIG_PCIE_UNIPHIER_EP) += pcie-uniphier-ep.o
>>  # depending on whether ACPI, the DT driver, or both are enabled.
>>  
>>  obj-$(CONFIG_PCIE_AL) += pcie-al.o
>> +obj-$(CONFIG_PCIE_TEGRA194) += pcie-tegra194.o
>>  obj-$(CONFIG_PCI_HISI) += pcie-hisi.o
> 
> It sounds like the interesting case is this:
> 
>   CONFIG_ARM64=y
>   CONFIG_ACPI=y
>   CONFIG_PCI_QUIRKS=y
>   CONFIG_PCIE_TEGRA194=m
> 
> I don't know how this works in this case:
> 
>   obj-$(CONFIG_PCIE_TEGRA194) += pcie-tegra194.o
>   obj-$(CONFIG_ARM64) += pcie-tegra194.o
> 
> We want tegra194_acpi_init() and the rest of the ECAM quirk to be
> compiled into the static kernel.  And we want tegra_pcie_dw_probe(),
> tegra_pcie_dw_remove(), etc, compiled into a module.
> 
> Does kbuild really compile pcie-tegra194.c twice?  And if so, it's not
> a problem that both the static kernel and the module contain a
> tegra194_pcie_ops symbol?

FWICT it does not compile it twice and I only see it builtin. We the
above I don't see any module generated.

>>  ifdef CONFIG_ACPI
>> diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
>> index b19775ab134e..ae70e53a7826 100644
>> --- a/drivers/pci/controller/dwc/pcie-tegra194.c
>> +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
>> @@ -240,13 +240,16 @@
>>  #define EP_STATE_DISABLED	0
>>  #define EP_STATE_ENABLED	1
>>  
>> +#if IS_ENABLED(CONFIG_PCIE_TEGRA194)
>>  static const unsigned int pcie_gen_freq[] = {
>>  	GEN1_CORE_CLK_FREQ,
>>  	GEN2_CORE_CLK_FREQ,
>>  	GEN3_CORE_CLK_FREQ,
>>  	GEN4_CORE_CLK_FREQ
>>  };
>> +#endif
> 
> This makes the minimal patch, but as Krzysztof suggests, I would
> prefer to move the whole struct so it's just inside the
> CONFIG_PCIE_TEGRA194 #ifdef.

OK, will do.

>> +#if defined(CONFIG_PCIEASPM)
>>  static const u32 event_cntr_ctrl_offset[] = {
>>  	0x1d8,
>>  	0x1a8,
>> @@ -264,6 +267,7 @@ static const u32 event_cntr_data_offset[] = {
>>  	0x1c8,
>>  	0x1dc
>>  };
>> +#endif
> 
> Similar for the CONFIG_PCIEASPM #ifdef.

OK.

Thanks
Jon

-- 
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