Re: [PATCH 5/5] VFIO: platform: VFIO platform Calxeda xgmac reset module

From: Alex Williamson
Date: Thu May 14 2015 - 11:14:20 EST

On Thu, 2015-05-14 at 11:06 +0200, Eric Auger wrote:
> Alex,
> On 05/13/2015 08:33 PM, Alex Williamson wrote:
> > On Thu, 2015-05-07 at 16:27 +0200, Eric Auger wrote:
> >> This patch introduces a module that registers and implements a basic
> >> reset function for the Calxeda xgmac device. This latter basically disables
> >> interrupts and stops DMA transfers.
> >>
> >> The reset function code is inherited from the native calxeda xgmac driver.
> >>
> >> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
> >> ---
> >> 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 | 121 +++++++++++++++++++++
> >> 5 files changed, 137 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..746b96b
> >> --- /dev/null
> >> +++ b/drivers/vfio/platform/reset/Kconfig
> >> @@ -0,0 +1,7 @@
> >> +config VFIO_PLATFORM_CALXEDAXGMAC_RESET
> >> + tristate "VFIO support for calxeda xgmac reset"
> >> + depends on VFIO_PLATFORM
> >> + help
> >> + Enables the VFIO platform driver to handle reset for Calxeda xgmac
> >> +
> >> + 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..2a486af
> >> --- /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_RESET) += 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..3c6e428
> >> --- /dev/null
> >> +++ b/drivers/vfio/platform/reset/vfio_platform_calxedaxgmac.c
> >> @@ -0,0 +1,121 @@
> >> +/*
> >> + * 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/io.h>
> >> +
> >> +#include "vfio_platform_private.h"
> >> +
> >> +#define DRIVER_VERSION "0.1"
> >> +#define DRIVER_AUTHOR "Eric Auger <eric.auger@xxxxxxxxxx>"
> >> +#define DRIVER_DESC "Reset support for Calxeda xgmac vfio platform device"
> >> +
> >> +#define CALXEDAXGMAC_COMPAT "calxeda,hb-xgmac"
> >> +
> >> +/* 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);
> >> +}
> >> +
> >> +int vfio_platform_calxedaxgmac_reset(struct vfio_platform_device *vdev)
> >> +{
> >> + struct vfio_platform_region reg = vdev->regions[0];
> >> +
> >> + if (!reg.ioaddr) {
> >> + reg.ioaddr =
> >> + ioremap_nocache(reg.addr, reg.size);
> >> + if (!reg.ioaddr)
> >> + return -ENOMEM;
> >> + }
> >> +
> >> + /* disable IRQ */
> >> + writel(0, reg.ioaddr + XGMAC_DMA_INTR_ENA);
> >> +
> >> + /* Disable the MAC core */
> >> + xgmac_mac_disable(reg.ioaddr);
> >> +
> >> + return 0;
> >> +}
> >> +EXPORT_SYMBOL_GPL(vfio_platform_calxedaxgmac_reset);
> >> +
> >> +static int __init vfio_platform_calxedaxgmac_init(void)
> >> +{
> >> + int (*register_reset)(char *, struct module *,
> >> + vfio_platform_reset_fn_t);
> >> + int ret;
> >> +
> >> + register_reset = symbol_get(vfio_platform_register_reset);
> >> + if (!register_reset)
> >> + return -EINVAL;
> >> +
> >> + ret = register_reset(CALXEDAXGMAC_COMPAT, THIS_MODULE,
> >> + vfio_platform_calxedaxgmac_reset);
> >> +
> >> + symbol_put(vfio_platform_register_reset);
> >> +
> >> + return ret;
> >> +}
> >> +
> >> +static void __exit vfio_platform_calxedaxgmac_exit(void)
> >> +{
> >> + int (*unregister_reset)(char *);
> >> + int ret;
> >> +
> >> + unregister_reset = symbol_get(vfio_platform_unregister_reset);
> >
> > Shouldn't we have gotten the symbol during the module init so that this
> > cannot fail?
> yes makes sense
> >
> >> + if (!unregister_reset)
> >> + return;
> >> +
> >> + ret = unregister_reset(CALXEDAXGMAC_COMPAT);
> >
> > unregister_reset() should just return void
> ok
> >
> >> +
> >> + symbol_put(vfio_platform_unregister_reset);
> >> +}
> >> +
> >> +module_init(vfio_platform_calxedaxgmac_init);
> >> +module_exit(vfio_platform_calxedaxgmac_exit);
> >> +
> >> +MODULE_VERSION(DRIVER_VERSION);
> >> +MODULE_LICENSE("GPL v2");
> >> +MODULE_AUTHOR(DRIVER_AUTHOR);
> >> +MODULE_DESCRIPTION(DRIVER_DESC);
> >
> >
> > So a user needs to manually load this module to get a working reset for
> > this device? That's never going to happen.
> The reset module is devised to be in-kernel or external. There is always
> the choice to include all reset modules as soon as vfio-platform /amba
> is chosen. What would be your preferred approach then? Do you consider
> this approach using separate reset modules is not sensible? Do you think
> we should put everything in the vfio-platform driver?

I respect your attempt to keep the code slim and modular by making the
reset functionality loadable, but we can't expect users to figure out
what module they need to load to make their device work. It needs to be
automatic. One way we could achieve that and still keep your premise of
loadable reset modules would be a lookup table in vfio-platform to
translate a device compatibility ID to a reset module name. We could
then do a request_module() to auto-load the reset module if one exists.
Maybe the ID table could even live in the reset driver, much like PCI
IDs live in those drivers. We also have the complication that there's
no direct module dependency for the reset module(s), so they would need
to be explicitly listed to install them into an initramfs.

If we take that approach, we're quickly building infrastructure that
gets more bloated than a few reset functions buried directly into
vfio-platform. Then we may wonder how many reset functions are we
reasonably going to get. If you don't have more than a couple in mind,
maybe we should just embed them into vfio-platform and worry about
creating something more dynamic when the need presents itself. Thanks,

Alex

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