linux-kernel - Re: [PATCH v3 7/7] PCI: endpoint: Add PCI Endpoint function driver for MHI bus

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Message-ID: <d25fdf75-e1fe-b83b-cb9c-ec0fb62f9254@amd.com>
Date:   Mon, 15 May 2023 13:37:28 +0530
From:   Kishon VijayAbraham I <kvijayab@....com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        lpieralisi@...nel.org, kw@...ux.com
Cc:     kishon@...nel.org, bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v3 7/7] PCI: endpoint: Add PCI Endpoint function driver
 for MHI bus

Hi Manivannan,

On 3/14/2023 10:16 AM, Manivannan Sadhasivam wrote:
> Add PCI Endpoint driver for the Qualcomm MHI (Modem Host Interface) bus.
> The driver implements the MHI function over PCI in the endpoint device
> such as SDX55 modem. The MHI endpoint function driver acts as a
> controller driver for the MHI Endpoint stack and carries out all PCI
> related activities like mapping the host memory using iATU, triggering
> MSIs etc...
> 
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---
>   drivers/pci/endpoint/functions/Kconfig       |  10 +
>   drivers/pci/endpoint/functions/Makefile      |   1 +
>   drivers/pci/endpoint/functions/pci-epf-mhi.c | 454 +++++++++++++++++++
>   3 files changed, 465 insertions(+)
>   create mode 100644 drivers/pci/endpoint/functions/pci-epf-mhi.c
> 
> diff --git a/drivers/pci/endpoint/functions/Kconfig b/drivers/pci/endpoint/functions/Kconfig
> index 9fd560886871..f5171b4fabbe 100644
> --- a/drivers/pci/endpoint/functions/Kconfig
> +++ b/drivers/pci/endpoint/functions/Kconfig
> @@ -37,3 +37,13 @@ config PCI_EPF_VNTB
>   	  between PCI Root Port and PCIe Endpoint.
>   
>   	  If in doubt, say "N" to disable Endpoint NTB driver.
> +
> +config PCI_EPF_MHI
> +	tristate "PCI Endpoint driver for MHI bus"
> +	depends on PCI_ENDPOINT && MHI_BUS_EP
> +	help
> +	   Enable this configuration option to enable the PCI Endpoint
> +	   driver for Modem Host Interface (MHI) bus in Qualcomm Endpoint
> +	   devices such as SDX55.
> +
> +	   If in doubt, say "N" to disable Endpoint driver for MHI bus.
> diff --git a/drivers/pci/endpoint/functions/Makefile b/drivers/pci/endpoint/functions/Makefile
> index 5c13001deaba..696473fce50e 100644
> --- a/drivers/pci/endpoint/functions/Makefile
> +++ b/drivers/pci/endpoint/functions/Makefile
> @@ -6,3 +6,4 @@
>   obj-$(CONFIG_PCI_EPF_TEST)		+= pci-epf-test.o
>   obj-$(CONFIG_PCI_EPF_NTB)		+= pci-epf-ntb.o
>   obj-$(CONFIG_PCI_EPF_VNTB) 		+= pci-epf-vntb.o
> +obj-$(CONFIG_PCI_EPF_MHI)		+= pci-epf-mhi.o
> diff --git a/drivers/pci/endpoint/functions/pci-epf-mhi.c b/drivers/pci/endpoint/functions/pci-epf-mhi.c
> new file mode 100644
> index 000000000000..03e7f42663b3
> --- /dev/null
> +++ b/drivers/pci/endpoint/functions/pci-epf-mhi.c
.
.
<snip>
.
.
> +static int pci_epf_mhi_link_up(struct pci_epf *epf)
> +{
> +	struct pci_epf_mhi *epf_mhi = epf_get_drvdata(epf);
> +	const struct pci_epf_mhi_ep_info *info = epf_mhi->info;
> +	struct mhi_ep_cntrl *mhi_cntrl = &epf_mhi->mhi_cntrl;
> +	struct pci_epc *epc = epf->epc;
> +	struct device *dev = &epf->dev;
> +	int ret;
> +
> +	mhi_cntrl->mmio = epf_mhi->mmio;
> +	mhi_cntrl->irq = epf_mhi->irq;
> +	mhi_cntrl->mru = info->mru;
> +
> +	/* Assign the struct dev of PCI EP as MHI controller device */
> +	mhi_cntrl->cntrl_dev = epc->dev.parent;
> +	mhi_cntrl->raise_irq = pci_epf_mhi_raise_irq;
> +	mhi_cntrl->alloc_map = pci_epf_mhi_alloc_map;
> +	mhi_cntrl->unmap_free = pci_epf_mhi_unmap_free;
> +	mhi_cntrl->read_from_host = pci_epf_mhi_read_from_host;
> +	mhi_cntrl->write_to_host = pci_epf_mhi_write_to_host;
> +
> +	/* Register the MHI EP controller */
> +	ret = mhi_ep_register_controller(mhi_cntrl, info->config);
> +	if (ret) {
> +		dev_err(dev, "Failed to register MHI EP controller: %d\n", ret);
> +		return ret;
> +	}

Any reason for delaying registration with MHI bus till link up? Since 
after linkup, the host can start using the device, this should be doing 
minimal stuff IMHO. Or is there further handshake between the host side 
MHI driver and the endpoint side MHI driver?

Thanks,
Kishon