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Message-ID: <20240904160422.gcyrdrzgc47w7pbd@thinkpad>
Date: Wed, 4 Sep 2024 21:34:22 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Johan Hovold <johan@...nel.org>
Cc: Richard Zhu <hongxing.zhu@....com>,
Lucas Stach <l.stach@...gutronix.de>,
Lorenzo Pieralisi <lpieralisi@...nel.org>,
Krzysztof Wilczyński <kw@...ux.com>,
Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
Shawn Guo <shawnguo@...nel.org>,
Sascha Hauer <s.hauer@...gutronix.de>,
Pengutronix Kernel Team <kernel@...gutronix.de>,
Fabio Estevam <festevam@...il.com>,
Jingoo Han <jingoohan1@...il.com>,
Chuanhua Lei <lchuanhua@...linear.com>,
Marek Vasut <marek.vasut+renesas@...il.com>,
Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
imx@...ts.linux.dev, linux-kernel@...r.kernel.org,
linux-renesas-soc@...r.kernel.org, linux-arm-msm@...r.kernel.org,
abel.vesa@...aro.org, johan+linaro@...nel.org,
Shashank Babu Chinta Venkata <quic_schintav@...cinc.com>
Subject: Re: [PATCH v6 4/4] PCI: qcom: Add RX margining settings for 16.0 GT/s
On Wed, Sep 04, 2024 at 11:53:42AM +0200, Johan Hovold wrote:
> On Wed, Sep 04, 2024 at 12:42:00PM +0530, Manivannan Sadhasivam via B4 Relay wrote:
> > From: Shashank Babu Chinta Venkata <quic_schintav@...cinc.com>
> >
> > Add RX lane margining settings for 16.0 GT/s (GEN 4) data rate. These
> > settings improve link stability while operating at high date rates and
> > helps to improve signal quality.
> >
> > Signed-off-by: Shashank Babu Chinta Venkata <quic_schintav@...cinc.com>
> > Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > [mani: dropped the code refactoring and minor changes]
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > ---
> > drivers/pci/controller/dwc/pcie-designware.h | 18 ++++++++++++++++
> > drivers/pci/controller/dwc/pcie-qcom-common.c | 31 +++++++++++++++++++++++++++
> > drivers/pci/controller/dwc/pcie-qcom-common.h | 1 +
> > drivers/pci/controller/dwc/pcie-qcom-ep.c | 4 +++-
> > drivers/pci/controller/dwc/pcie-qcom.c | 4 +++-
> > 5 files changed, 56 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> > index 51744ad25575..f5be99731f7e 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware.h
> > +++ b/drivers/pci/controller/dwc/pcie-designware.h
> > @@ -209,6 +209,24 @@
> >
> > #define PCIE_PL_CHK_REG_ERR_ADDR 0xB28
> >
> > +/*
> > + * 16.0 GT/s (GEN4) lane margining register definitions
>
> nit: Gen 4?
>
> > + */
> > +#define GEN4_LANE_MARGINING_1_OFF 0xb80
>
> nit: upper case hex
>
> > +#define MARGINING_MAX_VOLTAGE_OFFSET GENMASK(29, 24)
> > +#define MARGINING_NUM_VOLTAGE_STEPS GENMASK(22, 16)
> > +#define MARGINING_MAX_TIMING_OFFSET GENMASK(13, 8)
> > +#define MARGINING_NUM_TIMING_STEPS GENMASK(5, 0)
> > +
> > +#define GEN4_LANE_MARGINING_2_OFF 0xb84
>
> Same here
>
> > +#define MARGINING_IND_ERROR_SAMPLER BIT(28)
> > +#define MARGINING_SAMPLE_REPORTING_METHOD BIT(27)
> > +#define MARGINING_IND_LEFT_RIGHT_TIMING BIT(26)
> > +#define MARGINING_IND_UP_DOWN_VOLTAGE BIT(25)
> > +#define MARGINING_VOLTAGE_SUPPORTED BIT(24)
> > +#define MARGINING_MAXLANES GENMASK(20, 16)
> > +#define MARGINING_SAMPLE_RATE_TIMING GENMASK(13, 8)
> > +#define MARGINING_SAMPLE_RATE_VOLTAGE GENMASK(5, 0)
> > /*
> > * iATU Unroll-specific register definitions
> > * From 4.80 core version the address translation will be made by unroll
> > diff --git a/drivers/pci/controller/dwc/pcie-qcom-common.c b/drivers/pci/controller/dwc/pcie-qcom-common.c
> > index dc7d93db9dc5..99b75e7f085d 100644
> > --- a/drivers/pci/controller/dwc/pcie-qcom-common.c
> > +++ b/drivers/pci/controller/dwc/pcie-qcom-common.c
> > @@ -43,3 +43,34 @@ void qcom_pcie_common_set_16gt_eq_settings(struct dw_pcie *pci)
> > dw_pcie_writel_dbi(pci, GEN3_EQ_CONTROL_OFF, reg);
> > }
> > EXPORT_SYMBOL_GPL(qcom_pcie_common_set_16gt_eq_settings);
> > +
> > +void qcom_pcie_common_set_16gt_rx_margining_settings(struct dw_pcie *pci)
>
> I'd try to find a shorter symbol name here, "settings" seems redundant
> after "set". Perhaps just
>
> qcom_pcie_common_enable_lane_margining()
>
> or
>
> qcom_pcie_common_enable_16gt_lane_margining()?
>
This one looks better. Since lane margining is implemented in the receiver, we
don't really need 'rx' in the function name.
> if these settings are indeed specific to 16 GT/s. But perhaps it's
> better to let the helper honour pci->max_link_speed if different
> settings will later be needed for higher speeds:
>
> if (pcie_link_speed[pci->max_link_speed] >= PCIE_SPEED_16_0GT)
> qcom_pcie_common_enable_lane_margining(pci)
>
I did thought about it during the review, but this setting claims to be for 16
GT/s only. So I wouldn't recommend applying it to other speeds without checking
with Qcom.
Unfortunately, I'm on vacation for 2 weeks and have limited access to Qcom
internal docs/chat. So won't be able to check it soon. If Shashank could check
it, it is fine. But on the conservative side, let's stick to 16 GT/s only?
- Mani
> > void qcom_pcie_common_set_16gt_eq_settings(struct dw_pcie *pci);
> > +void qcom_pcie_common_set_16gt_rx_margining_settings(struct dw_pcie *pci);
>
> And maybe something similar for the eq settings for symmetry.
>
> Johan
--
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