Re: [RFC 3/3] VFIO: platform: add vfio-platform-calxedaxgmac driver

[Alex Williamson <alex.williamson@redhat.com>]

On Fri, 2015-04-17 at 15:37 +0200, Eric Auger wrote:
> This patch introduces a specialized vfio platform driver for the
> calxeda xgmac. On top of the generic vfio platform driver functionalities,
> it implements the reset modality.  This latter basically disables interrupts
> and stops DMA transfers.
> 
> Code is inherited from calxeda xgmac native driver
> 
> Signed-off-by: Eric Auger <eric.auger@linaro.org>
> ---
>  drivers/vfio/platform/Kconfig                      |   2 +
>  drivers/vfio/platform/Makefile                     |   2 +
>  drivers/vfio/platform/reset/Kconfig                |   7 ++
>  drivers/vfio/platform/reset/Makefile               |   5 +
>  .../platform/reset/vfio_platform_calxedaxgmac.c    | 109 +++++++++++++++++++++
>  5 files changed, 125 insertions(+)
>  create mode 100644 drivers/vfio/platform/reset/Kconfig
>  create mode 100644 drivers/vfio/platform/reset/Makefile
>  create mode 100644 drivers/vfio/platform/reset/vfio_platform_calxedaxgmac.c
> 
> diff --git a/drivers/vfio/platform/Kconfig b/drivers/vfio/platform/Kconfig
> index 9a4403e..1df7477 100644
> --- a/drivers/vfio/platform/Kconfig
> +++ b/drivers/vfio/platform/Kconfig
> @@ -18,3 +18,5 @@ config VFIO_AMBA
>  	  framework.
>  
>  	  If you don't know what to do here, say N.
> +
> +source "drivers/vfio/platform/reset/Kconfig"
> diff --git a/drivers/vfio/platform/Makefile b/drivers/vfio/platform/Makefile
> index 81de144..9ce8afe 100644
> --- a/drivers/vfio/platform/Makefile
> +++ b/drivers/vfio/platform/Makefile
> @@ -2,7 +2,9 @@
>  vfio-platform-y := vfio_platform.o vfio_platform_common.o vfio_platform_irq.o
>  
>  obj-$(CONFIG_VFIO_PLATFORM) += vfio-platform.o
> +obj-$(CONFIG_VFIO_PLATFORM) += reset/
>  
>  vfio-amba-y := vfio_amba.o
>  
>  obj-$(CONFIG_VFIO_AMBA) += vfio-amba.o
> +obj-$(CONFIG_VFIO_AMBA) += reset/
> diff --git a/drivers/vfio/platform/reset/Kconfig b/drivers/vfio/platform/reset/Kconfig
> new file mode 100644
> index 0000000..2c09cea
> --- /dev/null
> +++ b/drivers/vfio/platform/reset/Kconfig
> @@ -0,0 +1,7 @@
> +config VFIO_PLATFORM_CALXEDAXGMAC
> +	tristate "VFIO support for calxeda xgmac"
> +	depends on VFIO_PLATFORM
> +	help
> +	  Support for VFIO platform driver specialized for Calxeda xgmac reset.
> +
> +	  If you don't know what to do here, say N.
> diff --git a/drivers/vfio/platform/reset/Makefile b/drivers/vfio/platform/reset/Makefile
> new file mode 100644
> index 0000000..8977721
> --- /dev/null
> +++ b/drivers/vfio/platform/reset/Makefile
> @@ -0,0 +1,5 @@
> +vfio-platform-calxedaxgmac-y := vfio_platform_calxedaxgmac.o
> +
> +ccflags-y += -Idrivers/vfio/platform
> +
> +obj-$(CONFIG_VFIO_PLATFORM_CALXEDAXGMAC) += vfio-platform-calxedaxgmac.o
> diff --git a/drivers/vfio/platform/reset/vfio_platform_calxedaxgmac.c b/drivers/vfio/platform/reset/vfio_platform_calxedaxgmac.c
> new file mode 100644
> index 0000000..729d0cd
> --- /dev/null
> +++ b/drivers/vfio/platform/reset/vfio_platform_calxedaxgmac.c
> @@ -0,0 +1,109 @@
> +/*
> + * VFIO platform driver specialized for Calxeda xgmac reset
> + * reset code is inherited from calxeda xgmac native driver
> + *
> + * Copyright 2010-2011 Calxeda, Inc.
> + * Copyright (c) 2015 Linaro Ltd.
> + *              www.linaro.org
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms and conditions of the GNU General Public License,
> + * version 2, as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License along with
> + * this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/init.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +#include <linux/vfio.h>
> +#include "vfio_platform_private.h"
> +#include <linux/io.h>
> +
> +#define DRIVER_VERSION  "0.1"
> +#define DRIVER_AUTHOR   "Eric Auger <eric.auger@linaro.org>"
> +#define DRIVER_DESC     "VFIO - Calxeda xgmac vfio platform driver"
> +
> +/* XGMAC Register definitions */
> +#define XGMAC_CONTROL           0x00000000      /* MAC Configuration */
> +
> +/* DMA Control and Status Registers */
> +#define XGMAC_DMA_CONTROL       0x00000f18      /* Ctrl (Operational Mode) */
> +#define XGMAC_DMA_INTR_ENA      0x00000f1c      /* Interrupt Enable */
> +
> +/* DMA Control registe defines */
> +#define DMA_CONTROL_ST          0x00002000      /* Start/Stop Transmission */
> +#define DMA_CONTROL_SR          0x00000002      /* Start/Stop Receive */
> +
> +/* Common MAC defines */
> +#define MAC_ENABLE_TX           0x00000008      /* Transmitter Enable */
> +#define MAC_ENABLE_RX           0x00000004      /* Receiver Enable */
> +
> +static inline void xgmac_mac_disable(void __iomem *ioaddr)
> +{
> +	u32 value = readl(ioaddr + XGMAC_DMA_CONTROL);
> +
> +	value &= ~(DMA_CONTROL_ST | DMA_CONTROL_SR);
> +	writel(value, ioaddr + XGMAC_DMA_CONTROL);
> +
> +	value = readl(ioaddr + XGMAC_CONTROL);
> +	value &= ~(MAC_ENABLE_TX | MAC_ENABLE_RX);
> +	writel(value, ioaddr + XGMAC_CONTROL);
> +}
> +
> +static int vfio_platform_calxedaxgmac_reset(struct vfio_platform_device *vdev)
> +{
> +	struct resource *res = get_platform_resource(vdev, 0);
> +	void __iomem *base = phys_to_virt(res->start);
> +
> +	if (!base)
> +		return -ENOMEM;
> +
> +	/* disable IRQ */
> +	writel(0, base + XGMAC_DMA_INTR_ENA);
> +
> +	/* Disable the MAC core */
> +	xgmac_mac_disable(base);
> +
> +	return 0;
> +}
> +
> +static int vfio_platform_calxedaxgmac_probe(struct platform_device *pdev)
> +{
> +	int ret;
> +	struct vfio_device *vfio_dev;
> +	struct vfio_platform_device *vpdev;
> +
> +	ret = vfio_platform_probe(pdev);
> +	if (ret)
> +		return ret;
> +
> +	vfio_dev = vfio_device_get_from_dev(&pdev->dev),
> +	vpdev = (struct vfio_platform_device *) vfio_device_data(vfio_dev);
> +	vpdev->reset = vfio_platform_calxedaxgmac_reset;
> +
> +	return ret;
> +}
> +
> +static struct platform_driver vfio_platform_calxedaxgmac_driver = {
> +	.driver = {
> +		.name = "vfio-platform-calxedaxgmac",
> +	},
> +	.probe = vfio_platform_calxedaxgmac_probe,
> +	.remove = vfio_platform_remove,
> +};
> +
> +module_platform_driver(vfio_platform_calxedaxgmac_driver);
> +
> +MODULE_VERSION(DRIVER_VERSION);
> +MODULE_LICENSE("GPL v2");
> +MODULE_AUTHOR(DRIVER_AUTHOR);
> +MODULE_DESCRIPTION(DRIVER_DESC);

I don't really understand why this needs to be a new driver that wraps
around the vfio platform driver rather than just an entry in a table of
available device specific reset functions, setup through the normal
probe path.  Do we really have no clue what the device is to be able to
attach a reset function to it from the base vfio platform code?  This
also seems like a pain for users, who now need to figure out which
vfio_platform driver to bind to a given device.  If the user can figure
that out, why can't the kernel just pick the right reset callback for
them?  Thanks,

Alex