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Date:   Wed, 10 Aug 2022 14:47:26 -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
Message-ID: <YvQnbq2RhMOElQE3@google.com>
References: <20220727181936.3250466-1-saravanak@google.com>
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On Wed, Aug 10, 2022 at 05:58:58AM -0700, Guenter Roeck wrote:
> On 8/9/22 20:33, Saravana Kannan wrote:
> [ ... ]
> 
> > 
> > Can you give me more details on the qemu configuration so I could try
> > to reproduce it?
> 
> qemu-system-arm -M vexpress-a9 -kernel arch/arm/boot/zImage -no-reboot \
>     -initrd rootfs-armv5.cpio -m 128 \
>     --append "rdinit=/sbin/init console=ttyAMA0,115200" \
>     -dtb arch/arm/boot/dts/vexpress-v2p-ca9.dtb \
>     -nographic -monitor null -serial stdio
> 
> using multi_v7_defconfig will hang nicely with your patch applied,
> and boot as expected without. This was with qemu v7.0, but I am
> sure older qemu versions will show the same behavior. The initrd
> used should not matter, but you'll find it at
> https://github.com/groeck/linux-build-test/blob/master/rootfs/arm-v7/rootfs-armv5.cpio.gz
> 
> Guenter
>
Hi Guenter,

Thanks for the information; I was able to reproduce this on my end as
well. The following changes fixed the problem for me. Can you please try
them out?

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 70f79fc71539..b377f18d8acc 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -881,6 +881,11 @@ static int __device_attach_driver(struct device_driver *drv, void *_data)
                dev_dbg(dev, "Device match requests probe deferral\n");
                dev->can_match = true;
                driver_deferred_probe_add(dev);
+               /*
+                * Device can't match with the bus right now, so don't attempt
+                * to match or bind with other drivers on the bus.
+                */
+               return ret;
        } else if (ret < 0) {
                dev_dbg(dev, "Bus failed to match device: %d\n", ret);
                return ret;
@@ -1120,6 +1125,11 @@ static int __driver_attach(struct device *dev, void *data)
                dev_dbg(dev, "Device match requests probe deferral\n");
                dev->can_match = true;
                driver_deferred_probe_add(dev);
+               /*
+                * Driver could not match with device, but may match with
+                * another device on the bus.
+                */
+               return 0;
        } else if (ret < 0) {
                dev_dbg(dev, "Bus failed to match device: %d\n", ret);
                return ret;


Thanks,
Isaac