linux-kernel - Re: [PATCH v4 08/10] PCI: brcmstb: Adjust PHY PLL setup to use a 54MHz input refclk

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Message-ID: <f9f49030-0518-4e30-91a7-3c088c31180b@suse.de>
Date: Tue, 10 Dec 2024 15:42:21 +0200
From: Stanimir Varbanov <svarbanov@...e.de>
To: James Quinlan <james.quinlan@...adcom.com>,
 Stanimir Varbanov <svarbanov@...e.de>, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-rpi-kernel@...ts.infradead.org, linux-pci@...r.kernel.org,
 Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Florian Fainelli <florian.fainelli@...adcom.com>,
 Jim Quinlan <jim2101024@...il.com>,
 Nicolas Saenz Julienne <nsaenz@...nel.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>, kw@...ux.com,
 Philipp Zabel <p.zabel@...gutronix.de>,
 Andrea della Porta <andrea.porta@...e.com>,
 Phil Elwell <phil@...pberrypi.com>, Jonathan Bell <jonathan@...pberrypi.com>
Subject: Re: [PATCH v4 08/10] PCI: brcmstb: Adjust PHY PLL setup to use a
 54MHz input refclk

Hi Jim

On 12/10/24 12:52 AM, James Quinlan wrote:
> On 10/25/24 08:45, Stanimir Varbanov wrote:
>> The default input reference clock for the PHY PLL is 100Mhz, except for
>> some devices where it is 54Mhz like bcm2712C1 and bcm2712D0.
>>
>> To implement this adjustments introduce a new .post_setup op in
>> pcie_cfg_data and call it at the end of brcm_pcie_setup function.
>>
>> The bcm2712 .post_setup callback implements the required MDIO writes that
>> switch the PLL refclk and also change PHY PM clock period.
>>
>> Without this RPi5 PCIex1 is unable to enumerate endpoint devices on
>> the expansion connector.
>>
>> Signed-off-by: Stanimir Varbanov <svarbanov@...e.de>
>> ---
>> v3 -> v4:
>>   - Improved patch description (Florian)
>>
>>   drivers/pci/controller/pcie-brcmstb.c | 42 +++++++++++++++++++++++++++
>>   1 file changed, 42 insertions(+)
>>
>> diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/
>> controller/pcie-brcmstb.c
>> index d970a76aa9ef..2571dcc14560 100644
>> --- a/drivers/pci/controller/pcie-brcmstb.c
>> +++ b/drivers/pci/controller/pcie-brcmstb.c
>> @@ -55,6 +55,10 @@
>>   #define PCIE_RC_DL_MDIO_WR_DATA                0x1104
>>   #define PCIE_RC_DL_MDIO_RD_DATA                0x1108
>>   +#define PCIE_RC_PL_PHY_CTL_15                0x184c
>> +#define  PCIE_RC_PL_PHY_CTL_15_DIS_PLL_PD_MASK        0x400000
>> +#define  PCIE_RC_PL_PHY_CTL_15_PM_CLK_PERIOD_MASK    0xff
>> +
>>   #define PCIE_MISC_MISC_CTRL                0x4008
>>   #define  PCIE_MISC_MISC_CTRL_PCIE_RCB_64B_MODE_MASK    0x80
>>   #define  PCIE_MISC_MISC_CTRL_PCIE_RCB_MPS_MODE_MASK    0x400
>> @@ -251,6 +255,7 @@ struct pcie_cfg_data {
>>       u8 num_inbound_wins;
>>       int (*perst_set)(struct brcm_pcie *pcie, u32 val);
>>       int (*bridge_sw_init_set)(struct brcm_pcie *pcie, u32 val);
>> +    int (*post_setup)(struct brcm_pcie *pcie);
>>   };
>>     struct subdev_regulators {
>> @@ -826,6 +831,36 @@ static int brcm_pcie_perst_set_generic(struct
>> brcm_pcie *pcie, u32 val)
>>       return 0;
>>   }
>>   +static int brcm_pcie_post_setup_bcm2712(struct brcm_pcie *pcie)
>> +{
>> +    const u16 data[] = { 0x50b9, 0xbda1, 0x0094, 0x97b4, 0x5030,
>> 0x5030, 0x0007 };
>> +    const u8 regs[] = { 0x16, 0x17, 0x18, 0x19, 0x1b, 0x1c, 0x1e };
>> +    int ret, i;
>> +    u32 tmp;
>> +
>> +    /* Allow a 54MHz (xosc) refclk source */
>> +    ret = brcm_pcie_mdio_write(pcie->base, MDIO_PORT0,
>> SET_ADDR_OFFSET, 0x1600);
>> +    if (ret < 0)
>> +        return ret;
>> +
>> +    for (i = 0; i < ARRAY_SIZE(regs); i++) {
>> +        ret = brcm_pcie_mdio_write(pcie->base, MDIO_PORT0, regs[i],
>> data[i]);
>> +        if (ret < 0)
>> +            return ret;
>> +    }
>> +
>> +    usleep_range(100, 200);
>> +
>> +    /* Fix for L1SS errata */
>> +    tmp = readl(pcie->base + PCIE_RC_PL_PHY_CTL_15);
>> +    tmp &= ~PCIE_RC_PL_PHY_CTL_15_PM_CLK_PERIOD_MASK;
>> +    /* PM clock period is 18.52ns (round down) */
>> +    tmp |= 0x12;
>> +    writel(tmp, pcie->base + PCIE_RC_PL_PHY_CTL_15);
> 
> Hi Stan,
> 
> Can you please say more about where this errata came from?  I asked the
> 7712 PCIe HW folks and they said that there best guess was that it was a
> old workaround for a particular Broadcom Wifi endpoint.  Do you know its
> origin?

Unfortunately, I don't know the details. See the comments on previous
series version [1]. My observation shows that MDIO writes are
implemented in RPi platform firmware only for pcie2 (where RP1 south
bridge is connected) but not for pcie1 expansion connector.

~Stan

[1] https://www.spinics.net/lists/linux-pci/msg160842.html