linux-kernel - Re: [PATCH 5/8] PCI: rzg3s-host: Add Initial PCIe Host Driver for Renesas RZ/G3S SoC

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Message-ID: <b4771b63-3198-47c8-a83d-5133ba80d39b@tuxon.dev>
Date: Fri, 9 May 2025 14:41:44 +0300
From: Claudiu Beznea <claudiu.beznea@...on.dev>
To: Philipp Zabel <p.zabel@...gutronix.de>, bhelgaas@...gle.com,
 lpieralisi@...nel.org, kw@...ux.com, manivannan.sadhasivam@...aro.org,
 robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
 geert+renesas@...der.be, magnus.damm@...il.com, mturquette@...libre.com,
 sboyd@...nel.org, saravanak@...gle.com
Cc: linux-pci@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
 Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH 5/8] PCI: rzg3s-host: Add Initial PCIe Host Driver for
 Renesas RZ/G3S SoC

Hi, Philipp,

On 09.05.2025 13:51, Philipp Zabel wrote:
> Hi Claudiu,
> 
> On Mi, 2025-04-30 at 13:32 +0300, Claudiu wrote:
>> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>>
>> The Renesas RZ/G3S features a PCIe IP that complies with the PCI Express
>> Base Specification 4.0 and supports speeds of up to 5 GT/s. It functions
>> only as a root complex, with a single-lane (x1) configuration. The
>> controller includes Type 1 configuration registers, as well as IP
>> specific registers (called AXI registers) required for various adjustments.
>>
>> Other Renesas RZ SoCs (e.g., RZ/G3E, RZ/V2H) share the same AXI registers
>> but have both Root Complex and Endpoint capabilities. As a result, the PCIe
>> host driver can be reused for these variants with minimal adjustments.
>>
>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>> ---
>>  MAINTAINERS                              |    8 +
>>  drivers/pci/controller/Kconfig           |    7 +
>>  drivers/pci/controller/Makefile          |    1 +
>>  drivers/pci/controller/pcie-rzg3s-host.c | 1561 ++++++++++++++++++++++
>>  4 files changed, 1577 insertions(+)
>>  create mode 100644 drivers/pci/controller/pcie-rzg3s-host.c
>>
> [...]
>> diff --git a/drivers/pci/controller/pcie-rzg3s-host.c b/drivers/pci/controller/pcie-rzg3s-host.c
>> new file mode 100644
>> index 000000000000..c3bce0acd57e
>> --- /dev/null
>> +++ b/drivers/pci/controller/pcie-rzg3s-host.c
>> @@ -0,0 +1,1561 @@
> [...]
>> +static int rzg3s_pcie_resets_bulk_set(int (*action)(int num, struct reset_control_bulk_data *rstcs),
>> +				      struct reset_control **resets, u8 num_resets)
>> +{
>> +	struct reset_control_bulk_data *data __free(kfree) =
>> +		kcalloc(num_resets, sizeof(*data), GFP_KERNEL);
>> +
>> +	if (!data)
>> +		return -ENOMEM;
>> +
>> +	for (u8 i = 0; i < num_resets; i++)
>> +		data[i].rstc = resets[i];
>> +
>> +	return action(num_resets, data);
>> +}
> 
> What is the purpose of this? Can't you just store struct
> reset_control_bulk_data in struct rzg3s_pcie_host and call
> reset_control_bulk_assert/deassert() directly?

Yes, I can. I was trying to avoid storing also the reset_control_bulk_data
in struct rzg3s_pcie_host since all that is needed can be retrieved from
the already parsed in probe cfg_resets and power_resets.

> 
>> +static int
>> +rzg3s_pcie_resets_init(struct device *dev, struct reset_control ***resets,
>> +		       struct reset_control *(*action)(struct device *dev, const char *id),
>> +		       const char * const *reset_names, u8 num_resets)
>> +{
>> +	*resets = devm_kcalloc(dev, num_resets, sizeof(struct reset_control *), GFP_KERNEL);
>> +	if (!*resets)
>> +		return -ENOMEM;
>> +
>> +	for (u8 i = 0; i < num_resets; i++) {
>> +		(*resets)[i] = action(dev, reset_names[i]);
>> +		if (IS_ERR((*resets)[i]))
>> +			return PTR_ERR((*resets)[i]);
>> +	}
>> +
>> +	return 0;
>> +}
> 
> Why not use devm_reset_control_bulk_get_exclusive() directly?

I wasn't able to find a bulk_get_exclusive_deasserted() kind of API.

This IP needs particular sequence for configuration. First, after power on,
the following resets need to be de-asserted:

	const char * const power_resets[] = {
		"aresetn", "rst_cfg_b", "rst_load_b",
	};

then, after proper values are written into the configuration registers, the
rest of the resets need to be de-asserted:

	const char * const cfg_resets[] = {
		"rst_b", "rst_ps_b", "rst_gp_b", "rst_rsm_b",
	};

So I was trying to get and de-assert the power_resets in probe and just get
the cfg_resets in the 1st step of the initialization, and later to
de-assert the cfg_resets as well.

Now, after you pointed it out, maybe you are proposing to just
get_exclusive everything in one shot and then to de-assert what is needed
at proper moments with generic reset control APIs?

Thank you for your review,
Claudiu