Re: [PATCH V4] PCI: tegra: Fix building Tegra194 PCIe driver

[Jon Hunter <jonathanh@nvidia.com>]

Hi Bjorn, Lorenzo,

On 10/06/2021 10:07, Thierry Reding wrote:
> On Thu, Jun 10, 2021 at 07:41:34AM +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.
>> 2. 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
> 
> I think the correct way to write conditionals that are true on =y and =m
> is to use:
> 
> 	#ifdef IS_ENABLED(CONFIG_PCIE_TEGRA194)
> 
> but that doesn't fix the issue of not getting the quirks included when
> CONFIG_PCIE_TEGRA194=m.
> 
>>    driver. Given that the ACPI quirk code for Tegra194 is completely
>>    independent of the native Tegra194 PCIe driver, move this code into
>>    its own file so that it can be built independently and we can remove
>>    the "#ifdef CONFIG_PCIE_TEGRA194" in the native driver. Note that
>>    given the native Tegra194 PCIe driver is only used with device-tree,
>>    this will not cause any conflicts.
>> 3. The below build warnings to be seen with particular kernel
>>    configurations. Fix these by moving these structure definitions to
>>    within the necessary guards.
>>
>>   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>
>> ---
>> Changes since V3:
>> - Moved ACPI quirk code into separate source file
>>
>> Changes since V2:
>> - Update the commit message per Bjorn's feedback
>> - Moved the structure definitions within the necessary guards as opposed
>>   to wrapping the existing defintions with the appropriate guards.
>>
>> Changes since V1:
>> - Added fixes tag
>> - Fixed 'defined but not used' compiler warnings
>>
>>  drivers/pci/controller/dwc/Makefile           |   3 +-
>>  .../pci/controller/dwc/pcie-tegra194-acpi.c   | 108 ++++++++++++++
>>  drivers/pci/controller/dwc/pcie-tegra194.c    | 138 +++---------------
>>  3 files changed, 128 insertions(+), 121 deletions(-)
>>  create mode 100644 drivers/pci/controller/dwc/pcie-tegra194-acpi.c
> 
> We've had a similar problem with Tegra210 EMC and the EMC frequency
> table parsing code. The EMC frequency table parsing code needs to be
> always built-in because it is stashed into a linker section. However
> we still want the driver to be able to be a loadable module. The only
> way I know how to achieve that is by splitting up the sources files
> like you do here, so I this looks like a correct fix:
> 
> Reviewed-by: Thierry Reding <treding@nvidia.com>


Just a reminder that we need to get this fixed for v5.13. Please let me
know if you have any more comments on this fix.

Thanks!
Jon

-- 
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