Re: [PATCH v6 2/3] PCI: qcom: Define slot capabilities using PCI_EXP_SLTCAP_*

[Baruch Siach <baruch@tkos.co.il>]

Hi Pali,

On Thu, Jun 09 2022, Pali Rohár wrote:
> On Monday 07 February 2022 16:51:25 Baruch Siach wrote:
>> From: Baruch Siach <baruch.siach@siklu.com>
>> 
>> The PCIE_CAP_LINK1_VAL macro actually defines slot capabilities. Use
>> PCI_EXP_SLTCAP_* macros to spell its value, and rename it to better
>> describe its meaning.
>> 
>> Signed-off-by: Baruch Siach <baruch.siach@siklu.com>
>> ---
>>  drivers/pci/controller/dwc/pcie-qcom.c | 15 +++++++++++++--
>>  1 file changed, 13 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
>> index c19cd506ed3f..01e58b057d2a 100644
>> --- a/drivers/pci/controller/dwc/pcie-qcom.c
>> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
>> @@ -69,7 +69,18 @@
>>  #define PCIE20_AXI_MSTR_RESP_COMP_CTRL1		0x81c
>>  #define CFG_BRIDGE_SB_INIT			BIT(0)
>>  
>> -#define PCIE_CAP_LINK1_VAL			0x2FD7F
>> +#define PCIE_CAP_SLOT_POWER_LIMIT_VAL		0x7D00
>> +#define PCIE_CAP_SLOT_POWER_LIMIT_SCALE		0x8000
>
> Hello!
>
> Please do not use hardcoded values for slot power limit value and scale
> numbers. There are macros PCI_EXP_SLTCAP_SPLV and PCI_EXP_SLTCAP_SPLS
> for composing mask:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/pci_regs.h?h=v5.19-rc1#n593
> Which could be used together with FIELD_PREP(). See e.g. aardvark commit:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0d5b8c298545c827ca9f2461b2655277ce0aef79

Thanks for the tip.

> And the important information: Slot power limit is board specific and
> depends on how power supply and power regulators are designed. So slot
> power limit **cannot** be hardcoded in driver. Instead this value should
> be read from device tree file for the current board.
>
> There is a new kernel function of_pci_get_slot_power_limit() which reads
> it and compose PCIe slot power limit value and scale numbers. See:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/of.c?h=v5.19-rc1#n631

The 'slot-power-limit-milliwatt' property appears to be undocumented as
of v5.19-rc1.

This patch should make no functional change. I guess we should keep the
default hard-coded driver value for compatibility with existing DTs with
no 'slot-power-limit-milliwatt'.

Thanks,
baruch

>> +#define PCIE_CAP_SLOT_VAL			(PCI_EXP_SLTCAP_ABP | \
>> +						PCI_EXP_SLTCAP_PCP | \
>> +						PCI_EXP_SLTCAP_MRLSP | \
>> +						PCI_EXP_SLTCAP_AIP | \
>> +						PCI_EXP_SLTCAP_PIP | \
>> +						PCI_EXP_SLTCAP_HPS | \
>> +						PCI_EXP_SLTCAP_HPC | \
>> +						PCI_EXP_SLTCAP_EIP | \
>> +						PCIE_CAP_SLOT_POWER_LIMIT_VAL | \
>> +						PCIE_CAP_SLOT_POWER_LIMIT_SCALE)
>>  
>>  #define PCIE20_PARF_Q2A_FLUSH			0x1AC
>>  
>> @@ -1111,7 +1122,7 @@ static int qcom_pcie_init_2_3_3(struct qcom_pcie *pcie)
>>  
>>  	writel(PCI_COMMAND_MASTER, pci->dbi_base + PCI_COMMAND);
>>  	writel(DBI_RO_WR_EN, pci->dbi_base + PCIE20_MISC_CONTROL_1_REG);
>> -	writel(PCIE_CAP_LINK1_VAL, pci->dbi_base + offset + PCI_EXP_SLTCAP);
>> +	writel(PCIE_CAP_SLOT_VAL, pci->dbi_base + offset + PCI_EXP_SLTCAP);
>>  
>>  	val = readl(pci->dbi_base + offset + PCI_EXP_LNKCAP);
>>  	val &= ~PCI_EXP_LNKCAP_ASPMS;
>> -- 
>> 2.34.1
>> 


-- 
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