Re: [PATCH v2 15/15] phy: qcom-qmp-pcie: add support for sc8280xp 4-lane PHYs

[Dmitry Baryshkov <dmitry.baryshkov@linaro.org>]

On 20/10/2022 09:43, Johan Hovold wrote:
> On Thu, Oct 20, 2022 at 06:43:47AM +0300, Dmitry Baryshkov wrote:
>> On 19/10/2022 14:35, Johan Hovold wrote:
>>> The PCIe2 and PCIe3 controllers and PHYs on SC8280XP can be used in
>>> 4-lane mode or as separate controllers and PHYs in 2-lane mode (e.g. as
>>> PCIe2A and PCIe2B).
>>>
>>> Add support for fetching the 4-lane configuration from the TCSR and
>>> programming the lane registers of the second port when in 4-lane mode.
>>>
>>> Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
>>> ---
>>>    drivers/phy/qualcomm/Kconfig             |   1 +
>>>    drivers/phy/qualcomm/phy-qcom-qmp-pcie.c | 118 +++++++++++++++++++++++
>>>    2 files changed, 119 insertions(+)
>>>
>>> diff --git a/drivers/phy/qualcomm/Kconfig b/drivers/phy/qualcomm/Kconfig
>>> index 5c98850f5a36..eb9ddc685b38 100644
>>> --- a/drivers/phy/qualcomm/Kconfig
>>> +++ b/drivers/phy/qualcomm/Kconfig
>>> @@ -54,6 +54,7 @@ config PHY_QCOM_QMP
>>>    	tristate "Qualcomm QMP PHY Driver"
>>>    	depends on OF && COMMON_CLK && (ARCH_QCOM || COMPILE_TEST)
>>>    	select GENERIC_PHY
>>> +	select MFD_SYSCON
>>>    	help
>>>    	  Enable this to support the QMP PHY transceiver that is used
>>>    	  with controllers such as PCIe, UFS, and USB on Qualcomm chips.
>>> diff --git a/drivers/phy/qualcomm/phy-qcom-qmp-pcie.c b/drivers/phy/qualcomm/phy-qcom-qmp-pcie.c
>>> index ea5228bd9ecc..e5bce4810bb5 100644
>>> --- a/drivers/phy/qualcomm/phy-qcom-qmp-pcie.c
>>> +++ b/drivers/phy/qualcomm/phy-qcom-qmp-pcie.c
>>> @@ -10,6 +10,7 @@
>>>    #include <linux/io.h>
>>>    #include <linux/iopoll.h>
>>>    #include <linux/kernel.h>
>>> +#include <linux/mfd/syscon.h>
>>>    #include <linux/module.h>
>>>    #include <linux/of.h>
>>>    #include <linux/of_device.h>
>>> @@ -17,6 +18,7 @@
>>>    #include <linux/phy/pcie.h>
>>>    #include <linux/phy/phy.h>
>>>    #include <linux/platform_device.h>
>>> +#include <linux/regmap.h>
>>>    #include <linux/regulator/consumer.h>
>>>    #include <linux/reset.h>
>>>    #include <linux/slab.h>
>>> @@ -886,6 +888,10 @@ static const struct qmp_phy_init_tbl sc8280xp_qmp_gen3x2_pcie_rc_serdes_tbl[] =
>>>    	QMP_PHY_INIT_CFG(QSERDES_V5_COM_BIAS_EN_CLKBUFLR_EN, 0x14),
>>>    };
>>>    
>>> +static const struct qmp_phy_init_tbl sc8280xp_qmp_gen3x4_pcie_serdes_4ln_tbl[] = {
>>> +	QMP_PHY_INIT_CFG(QSERDES_V5_COM_BIAS_EN_CLKBUFLR_EN, 0x1c),
>>> +};
>>> +
>>>    static const struct qmp_phy_init_tbl sc8280xp_qmp_gen3x1_pcie_tx_tbl[] = {
>>>    	QMP_PHY_INIT_CFG(QSERDES_V5_TX_PI_QEC_CTRL, 0x20),
>>>    	QMP_PHY_INIT_CFG(QSERDES_V5_TX_LANE_MODE_1, 0x75),
>>> @@ -1491,6 +1497,9 @@ struct qmp_phy_cfg {
>>>    	const struct qmp_phy_cfg_tables *tables_rc;
>>>    	const struct qmp_phy_cfg_tables *tables_ep;
>>>    
>>> +	const struct qmp_phy_init_tbl *serdes_4ln_tbl;
>>> +	int serdes_4ln_num;
>>
>> Would it make more sense to change this into the proper
>> qmp_phy_cfg_tables entry and then use the existing API for programming
>> the table?
> 
> No, there is just one serdes register update needed when in 4-lane mode,
> besides programming tx/rx for the second port. Adding a third struct
> qmp_phy_cfg_tables for this seems like overkill and would lead to a more
> convoluted implementation of the programming sequence.

Ack. Let's have it this way and change it later if the need arises.

> 
> And you can't add it two one of the existing ones, as your comment seems
> to suggest.

Please excuse me if I didn't write it clear enough. I suggested adding 
another cfg_tables, as you correctly commented above.

> 
> The gen3x4 PHYs can be in either 4-lane or 2-lane mode depending on the
> TCSR configuration. Port A is programmed identically in both cases
> except for this serdes register, and in 4-lane mode tx/rx also needs
> to be programmed for port B.
>   
>>> +
>>>    	/* clock ids to be requested */
>>>    	const char * const *clk_list;
>>>    	int num_clks;
>>> @@ -1518,6 +1527,7 @@ struct qmp_pcie {
>>>    	struct device *dev;
>>>    
>>>    	const struct qmp_phy_cfg *cfg;
>>> +	bool tcsr_4ln_config;
>>
>> As a matter of preference, this seems too specific. I'd rename it to
>> split_config or split_4ln_config.
> 
> I'm afraid those names do not make much sense. This TCSR register
> controls whether the PHY is in 4-lane mode (instead of 2-lane mode).

Well, we just need the info that it's 4-lane. It doesn't really matter 
if this information comes from TCSR, DT or e.g. fuses. I'd say that TCSR 
is a platform detail. Thus I'm suggesting a more generic name.

> 
>>>    
>>>    	void __iomem *serdes;
>>>    	void __iomem *pcs;
>>> @@ -1527,6 +1537,8 @@ struct qmp_pcie {
>>>    	void __iomem *tx2;
>>>    	void __iomem *rx2;
>>>    
>>> +	void __iomem *port_b;
>>> +
>>>    	struct clk *pipe_clk;
>>>    	struct clk *pipediv2_clk;
>>>    	struct clk_bulk_data *clks;
>>> @@ -1932,6 +1944,44 @@ static const struct qmp_phy_cfg sc8280xp_qmp_gen3x2_pciephy_cfg = {
>>>    	.phy_status		= PHYSTATUS,
>>>    };
>    
>>> +static void qmp_pcie_init_port_b(struct qmp_pcie *qmp, const struct qmp_phy_cfg_tables *tbls)
>>> +{
>>> +	const struct qmp_phy_cfg *cfg = qmp->cfg;
>>> +	const struct qmp_pcie_offsets *offs = cfg->offsets;
>>> +	void __iomem *tx3, *rx3, *tx4, *rx4;
>>> +
>>> +	tx3 = qmp->port_b + offs->tx;
>>> +	rx3 = qmp->port_b + offs->rx;
>>> +	tx4 = qmp->port_b + offs->tx2;
>>> +	rx4 = qmp->port_b + offs->rx2;
>>> +
>>> +	qmp_pcie_configure_lane(tx3, tbls->tx, tbls->tx_num, 1);
>>> +	qmp_pcie_configure_lane(rx3, tbls->rx, tbls->rx_num, 1);
>>> +
>>> +	qmp_pcie_configure_lane(tx4, tbls->tx, tbls->tx_num, 2);
>>> +	qmp_pcie_configure_lane(rx4, tbls->rx, tbls->rx_num, 2);
>>
>> I'd use BIT(2) and BIT(3) here. This would allow one to make a
>> difference between programming first pair of lanes and second pair of
>> lanes if necessary.
> 
> No, the tx and tx registers of the second port should be programmed
> identically to that of the first port.

As you would prefer. As a matter of fact, we do not have CFG_LANES in 
the PCIe PHY. Thus I'm surprised that you didn't drop this. I think 
CFG_LANES usage is limited to sm8250 USB and combo PHY configurations.

> 
>>> +}
>>> +
>>>    static void qmp_pcie_init_registers(struct qmp_pcie *qmp, const struct qmp_phy_cfg_tables *tbls)
>>>    {
>>>    	const struct qmp_phy_cfg *cfg = qmp->cfg;
>>> @@ -2080,6 +2148,11 @@ static void qmp_pcie_init_registers(struct qmp_pcie *qmp, const struct qmp_phy_c
>>>    
>>>    	qmp_pcie_configure(pcs, tbls->pcs, tbls->pcs_num);
>>>    	qmp_pcie_configure(pcs_misc, tbls->pcs_misc, tbls->pcs_misc_num);
>>> +
>>> +	if (cfg->lanes >= 4 && qmp->tcsr_4ln_config) {
>>> +		qmp_pcie_configure(serdes, cfg->serdes_4ln_tbl, cfg->serdes_4ln_num);
>>> +		qmp_pcie_init_port_b(qmp, tbls);
>>> +	}
>>
>> As you have been refactoring this piece of code, maybe it would make
>> more sense to change qmp->tx/tx2 into an array of two elements? Then we
>> can extend it to 4 in this patch, and just always write the whole array
>> in a loop?
> 
> No, I don't think that would be an improvement and would obscure the
> fact that we're programming two otherwise identical ports (e.g. tx1 and
> tx2 of port B is used for the third and fourth lanes).
> 
> Note that the above conditional encodes the difference in programming
> sequence between 4-lane and 2-lane mode I described above (one serdes
> register difference + tx/rx of port b).

Either way looks fine to me. So, let's leave this in a way you've 
implemented it.

-- 
With best wishes
Dmitry