Re: [Patch v6 8/9] PCI: tegra194: Add interconnect support in Tegra234

Lorenzo Pieralisi
2023-04-13T14:52:21Z

On Tue, Apr 11, 2023 at 04:30:01PM +0530, Sumit Gupta wrote:
> Add support to request DRAM bandwidth with Memory Interconnect
> in Tegra234 SoC. The DRAM BW required for different modes depends
> on speed (Gen-1/2/3/4) and width/lanes (x1/x2/x4/x8).
> Currently, no latency is observed in data transfer with PCI as the
> DRAM Freq is always set to max. But that results in high power
> consumption. Now for Tegra234, we are enabling the dynamic scaling
> of the DRAM Freq based on requests from Clients instead of running
> at the max Freq always. This change does that for PCI MC client.

I am sorry but this is still unclear to me. The sentence above makes
me think that you are *adding* latency to the data transfer trading
it with lower power consumption; probably that's a wrong parsing of
what you are saying - so please explain what you want to say
with "no latency is observed" and whether this patch changes that
(which is not allowed because that would count as a regression).

Thanks,
Lorenzo

>
> Suggested-by: Manikanta Maddireddy <mmaddireddy@nvidia.com>
> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
> ---
> drivers/pci/controller/dwc/pcie-tegra194.c | 51 +++++++++++++++-------
> 1 file changed, 35 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
> index e6eec85480ca..4fdadc7b045f 100644
> --- a/drivers/pci/controller/dwc/pcie-tegra194.c
> +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
> @@ -14,6 +14,7 @@
> #include <linux/delay.h>
> #include <linux/gpio.h>
> #include <linux/gpio/consumer.h>
> +#include <linux/interconnect.h>
> #include <linux/interrupt.h>
> #include <linux/iopoll.h>
> #include <linux/kernel.h>
> @@ -288,6 +289,7 @@ struct tegra_pcie_dw {
> unsigned int pex_rst_irq;
> int ep_state;
> long link_status;
> + struct icc_path *icc_path;
> };
>
> static inline struct tegra_pcie_dw *to_tegra_pcie(struct dw_pcie *pci)
> @@ -310,6 +312,27 @@ struct tegra_pcie_soc {
> enum dw_pcie_device_mode mode;
> };
>
> +static void tegra_pcie_icc_set(struct tegra_pcie_dw *pcie)
> +{
> + struct dw_pcie *pci = &pcie->pci;
> + u32 val, speed, width;
> +
> + val = dw_pcie_readw_dbi(pci, pcie->pcie_cap_base + PCI_EXP_LNKSTA);
> +
> + speed = FIELD_GET(PCI_EXP_LNKSTA_CLS, val);
> + width = FIELD_GET(PCI_EXP_LNKSTA_NLW, val);
> +
> + val = width * (PCIE_SPEED2MBS_ENC(pcie_link_speed[speed]) / BITS_PER_BYTE);
> +
> + if (icc_set_bw(pcie->icc_path, MBps_to_icc(val), 0))
> + dev_err(pcie->dev, "can't set bw[%u]\n", val);
> +
> + if (speed >= ARRAY_SIZE(pcie_gen_freq))
> + speed = 0;
> +
> + clk_set_rate(pcie->core_clk, pcie_gen_freq[speed]);
> +}
> +
> static void apply_bad_link_workaround(struct dw_pcie_rp *pp)
> {
> struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> @@ -453,18 +476,12 @@ static irqreturn_t tegra_pcie_ep_irq_thread(int irq, void *arg)
> struct tegra_pcie_dw *pcie = arg;
> struct dw_pcie_ep *ep = &pcie->pci.ep;
> struct dw_pcie *pci = &pcie->pci;
> - u32 val, speed;
> + u32 val;
>
> if (test_and_clear_bit(0, &pcie->link_status))
> dw_pcie_ep_linkup(ep);
>
> - speed = dw_pcie_readw_dbi(pci, pcie->pcie_cap_base + PCI_EXP_LNKSTA) &
> - PCI_EXP_LNKSTA_CLS;
> -
> - if (speed >= ARRAY_SIZE(pcie_gen_freq))
> - speed = 0;
> -
> - clk_set_rate(pcie->core_clk, pcie_gen_freq[speed]);
> + tegra_pcie_icc_set(pcie);
>
> if (pcie->of_data->has_ltr_req_fix)
> return IRQ_HANDLED;
> @@ -950,9 +967,9 @@ static int tegra_pcie_dw_host_init(struct dw_pcie_rp *pp)
>
> static int tegra_pcie_dw_start_link(struct dw_pcie *pci)
> {
> - u32 val, offset, speed, tmp;
> struct tegra_pcie_dw *pcie = to_tegra_pcie(pci);
> struct dw_pcie_rp *pp = &pci->pp;
> + u32 val, offset, tmp;
> bool retry = true;
>
> if (pcie->of_data->mode == DW_PCIE_EP_TYPE) {
> @@ -1023,13 +1040,7 @@ static int tegra_pcie_dw_start_link(struct dw_pcie *pci)
> goto retry_link;
> }
>
> - speed = dw_pcie_readw_dbi(pci, pcie->pcie_cap_base + PCI_EXP_LNKSTA) &
> - PCI_EXP_LNKSTA_CLS;
> -
> - if (speed >= ARRAY_SIZE(pcie_gen_freq))
> - speed = 0;
> -
> - clk_set_rate(pcie->core_clk, pcie_gen_freq[speed]);
> + tegra_pcie_icc_set(pcie);
>
> tegra_pcie_enable_interrupts(pp);
>
> @@ -2233,6 +2244,14 @@ static int tegra_pcie_dw_probe(struct platform_device *pdev)
>
> platform_set_drvdata(pdev, pcie);
>
> + pcie->icc_path = devm_of_icc_get(&pdev->dev, "write");
> + ret = PTR_ERR_OR_ZERO(pcie->icc_path);
> + if (ret) {
> + tegra_bpmp_put(pcie->bpmp);
> + dev_err_probe(&pdev->dev, ret, "failed to get write interconnect\n");
> + return ret;
> + }
> +
> switch (pcie->of_data->mode) {
> case DW_PCIE_RC_TYPE:
> ret = devm_request_irq(dev, pp->irq, tegra_pcie_rp_irq_handler,
> --
> 2.17.1
>