linux-kernel - Re: [PATCH v2 2/8] VMCI: dma dg: add MMIO access to registers

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Message-ID: <58BCE45B-E4FE-42BA-8A0C-32FFEA991B86@vmware.com>
Date:   Mon, 7 Feb 2022 08:51:15 +0000
From:   Jorgen Hansen <jhansen@...are.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        Pv-drivers <Pv-drivers@...are.com>,
        Vishnu Dasa <vdasa@...are.com>
Subject: Re: [PATCH v2 2/8] VMCI: dma dg: add MMIO access to registers



> On 4 Feb 2022, at 16.12, Greg KH <gregkh@...uxfoundation.org> wrote:
> 
> On Thu, Feb 03, 2022 at 05:12:31AM -0800, Jorgen Hansen wrote:
>> Detect the support for MMIO access through examination of the length
>> of the region requested in BAR1. If it is 256KB, the VMCI device
>> supports MMIO access to registers.
>> 
>> If MMIO access is supported, map the area of the region used for
>> MMIO access (64KB size at offset 128KB).
>> 
>> Add wrapper functions for accessing 32 bit register accesses through
>> either MMIO or IO ports based on device configuration.
>> 
>> Sending and receiving datagrams through iowrite8_rep/ioread8_rep is
>> left unchanged for now, and will be addressed in a later change.
>> 
>> Reviewed-by: Vishnu Dasa <vdasa@...are.com>
>> Signed-off-by: Jorgen Hansen <jhansen@...are.com>
>> ---
>> drivers/misc/vmw_vmci/vmci_guest.c | 68 ++++++++++++++++++++++--------
>> include/linux/vmw_vmci_defs.h      | 12 ++++++
>> 2 files changed, 62 insertions(+), 18 deletions(-)
>> 
>> diff --git a/drivers/misc/vmw_vmci/vmci_guest.c b/drivers/misc/vmw_vmci/vmci_guest.c
>> index 1018dc77269d..38ee7ed32ab9 100644
>> --- a/drivers/misc/vmw_vmci/vmci_guest.c
>> +++ b/drivers/misc/vmw_vmci/vmci_guest.c
>> @@ -45,6 +45,7 @@ static u32 vm_context_id = VMCI_INVALID_ID;
>> struct vmci_guest_device {
>> 	struct device *dev;	/* PCI device we are attached to */
>> 	void __iomem *iobase;
>> +	void __iomem *mmio_base;
>> 
>> 	bool exclusive_vectors;
>> 
>> @@ -89,6 +90,21 @@ u32 vmci_get_vm_context_id(void)
>> 	return vm_context_id;
>> }
>> 
>> +static unsigned int vmci_read_reg(struct vmci_guest_device *dev, u32 reg)
>> +{
>> +	if (dev->mmio_base != NULL)
>> +		return readl(dev->mmio_base + reg);
>> +	return ioread32(dev->iobase + reg);
>> +}
>> +
>> +static void vmci_write_reg(struct vmci_guest_device *dev, u32 val, u32 reg)
>> +{
>> +	if (dev->mmio_base != NULL)
>> +		writel(val, dev->mmio_base + reg);
>> +	else
>> +		iowrite32(val, dev->iobase + reg);
>> +}
>> +
>> /*
>>  * VM to hypervisor call mechanism. We use the standard VMware naming
>>  * convention since shared code is calling this function as well.
>> @@ -116,7 +132,7 @@ int vmci_send_datagram(struct vmci_datagram *dg)
>> 	if (vmci_dev_g) {
>> 		iowrite8_rep(vmci_dev_g->iobase + VMCI_DATA_OUT_ADDR,
>> 			     dg, VMCI_DG_SIZE(dg));
>> -		result = ioread32(vmci_dev_g->iobase + VMCI_RESULT_LOW_ADDR);
>> +		result = vmci_read_reg(vmci_dev_g, VMCI_RESULT_LOW_ADDR);
>> 	} else {
>> 		result = VMCI_ERROR_UNAVAILABLE;
>> 	}
>> @@ -384,7 +400,7 @@ static irqreturn_t vmci_interrupt(int irq, void *_dev)
>> 		unsigned int icr;
>> 
>> 		/* Acknowledge interrupt and determine what needs doing. */
>> -		icr = ioread32(dev->iobase + VMCI_ICR_ADDR);
>> +		icr = vmci_read_reg(dev, VMCI_ICR_ADDR);
>> 		if (icr == 0 || icr == ~0)
>> 			return IRQ_NONE;
>> 
>> @@ -429,7 +445,8 @@ static int vmci_guest_probe_device(struct pci_dev *pdev,
>> 				   const struct pci_device_id *id)
>> {
>> 	struct vmci_guest_device *vmci_dev;
>> -	void __iomem *iobase;
>> +	void __iomem *iobase = NULL;
>> +	void __iomem *mmio_base = NULL;
>> 	unsigned int capabilities;
>> 	unsigned int caps_in_use;
>> 	unsigned long cmd;
>> @@ -445,16 +462,32 @@ static int vmci_guest_probe_device(struct pci_dev *pdev,
>> 		return error;
>> 	}
>> 
>> -	error = pcim_iomap_regions(pdev, 1 << 0, KBUILD_MODNAME);
>> -	if (error) {
>> -		dev_err(&pdev->dev, "Failed to reserve/map IO regions\n");
>> -		return error;
>> +	/*
>> +	 * The VMCI device with mmio access to registers requests 256KB
>> +	 * for BAR1. If present, driver will use new VMCI device
>> +	 * functionality for register access and datagram send/recv.
>> +	 */
>> +
>> +	if (pci_resource_len(pdev, 1) == VMCI_WITH_MMIO_ACCESS_BAR_SIZE) {
>> +		dev_info(&pdev->dev, "MMIO register access is available\n");
>> +		mmio_base = pci_iomap_range(pdev, 1, VMCI_MMIO_ACCESS_OFFSET,
>> +					    VMCI_MMIO_ACCESS_SIZE);
>> +		/* If the map fails, we fall back to IOIO access. */
>> +		if (!mmio_base)
>> +			dev_warn(&pdev->dev, "Failed to map MMIO register access\n");
>> 	}
>> 
>> -	iobase = pcim_iomap_table(pdev)[0];
>> +	if (!mmio_base) {
>> +		error = pcim_iomap_regions(pdev, BIT(0), KBUILD_MODNAME);
>> +		if (error) {
>> +			dev_err(&pdev->dev, "Failed to reserve/map IO regions\n");
>> +			return error;
>> +		}
>> +		iobase = pcim_iomap_table(pdev)[0];
>> +	}
>> 
>> -	dev_info(&pdev->dev, "Found VMCI PCI device at %#lx, irq %u\n",
>> -		 (unsigned long)iobase, pdev->irq);
>> +	dev_info(&pdev->dev, "Found VMCI PCI device at %#lx, %#lx, irq %u\n",
>> +		 (unsigned long)iobase, (unsigned long)mmio_base, pdev->irq);
> 
> Why are you printing iomem addresses to userspace?  Are you sure that is
> ok?  Who is going to use it?

I’m not sure if there was a specific purpose back when this was added - most
likely the intention was simply to report the resources allocated to the device.
I'll remove this one too.

Thanks,
Jorgen