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Date:   Mon, 15 Aug 2022 11:43:10 -0700
From:   Isaac Manjarres <isaacmanjarres@google.com>
To:     Guenter Roeck <linux@roeck-us.net>
Cc:     Saravana Kannan <saravanak@google.com>,
        Russell King <linux@armlinux.org.uk>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Rob Herring <robh@kernel.org>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Sudeep Holla <sudeep.holla@arm.com>,
        Nicolas Saenz Julienne <nsaenz@kernel.org>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        patches@armlinux.org.uk, kernel-team@android.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6] amba: Remove deferred device addition
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On Fri, Aug 12, 2022 at 08:30:46AM -0700, Guenter Roeck wrote:
> After more testing: the changes above result in qemu sx1 boot failures.
> There is no crash, boot just hangs.
> 
> qemu command line:
> 
> qemu-system-arm -M sx1 -kernel arch/arm/boot/zImage -no-reboot \
> 	-initrd rootfs-armv4.cpio \
> 	--append "rdinit=/sbin/init console=ttyS0,115200 earlycon=uart8250,mmio32,0xfffb0000,115200n8" \
> 	-nographic -monitor null -serial stdio
> 
> with configuration from
> https://github.com/groeck/linux-build-test/blob/master/rootfs/arm/qemu_sx1_defconfig
> and root file system from
> https://github.com/groeck/linux-build-test/blob/master/rootfs/arm/rootfs-armv4.cpio.gz
> 
> This is with your other patch applied.
> 
> Guenter

Thanks for testing out the patch and sharing the qemu commandline you
used for the new issue. I was able to reproduce it on my end :) Can you
please try the following patch instead of the second patch I gave you?
This worked for me on sx1 and versatileab:

diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
index 32b0e0b930c1..110a535648d2 100644
--- a/drivers/amba/bus.c
+++ b/drivers/amba/bus.c
@@ -209,6 +209,7 @@ static int amba_match(struct device *dev, struct device_driver *drv)
        struct amba_device *pcdev = to_amba_device(dev);
        struct amba_driver *pcdrv = to_amba_driver(drv);

+       mutex_lock(&pcdev->periphid_lock);
        if (!pcdev->periphid) {
                int ret = amba_read_periphid(pcdev);

@@ -218,11 +219,14 @@ static int amba_match(struct device *dev, struct device_driver *drv)
                 * permanent failure in reading pid and cid, simply map it to
                 * -EPROBE_DEFER.
                 */
-               if (ret)
+               if (ret) {
+                       mutex_unlock(&pcdev->periphid_lock);
                        return -EPROBE_DEFER;
+               }
                dev_set_uevent_suppress(dev, false);
                kobject_uevent(&dev->kobj, KOBJ_ADD);
        }
+       mutex_unlock(&pcdev->periphid_lock);

        /* When driver_override is set, only bind to the matching driver */
        if (pcdev->driver_override)
@@ -532,6 +536,7 @@ static void amba_device_release(struct device *dev)

        if (d->res.parent)
                release_resource(&d->res);
+       mutex_destroy(&d->periphid_lock);
        kfree(d);
 }

@@ -584,6 +589,7 @@ static void amba_device_initialize(struct amba_device *dev, const char *name)
        dev->dev.dma_mask = &dev->dev.coherent_dma_mask;
        dev->dev.dma_parms = &dev->dma_parms;
        dev->res.name = dev_name(&dev->dev);
+       mutex_init(&dev->periphid_lock);
 }

 /**
diff --git a/include/linux/amba/bus.h b/include/linux/amba/bus.h
index e94cdf235f1d..5001e14c5c06 100644
--- a/include/linux/amba/bus.h
+++ b/include/linux/amba/bus.h
@@ -67,6 +67,7 @@ struct amba_device {
        struct clk              *pclk;
        struct device_dma_parameters dma_parms;
        unsigned int            periphid;
+       struct mutex            periphid_lock;
        unsigned int            cid;
        struct amba_cs_uci_id   uci;
        unsigned int            irq[AMBA_NR_IRQS];


Thanks,
Isaac