Re: [PATCH] MMC: fix sdhci-dove removal

Russell King - ARM Linux
2012-10-15T10:45:02Z

On Mon, Oct 15, 2012 at 11:37:25AM +0100, Russell King - ARM Linux wrote:
> On Mon, Oct 15, 2012 at 10:43:48AM +0100, Russell King - ARM Linux wrote:
> > 1. Unregister the device _BEFORE_ taking away any resources it may
> > be using.
> > 2. Don't check clks against NULL.
> >
> > Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
>
> Looking at this driver some more, who the hell came up with the sdhci
> registration interface? It violates one of the most fundamental
> principles of kernel driver programming. You do _NOT_ publish your
> driver interfaces _UNTIL_ you have finished setting your device up.
> Otherwise, in a preemptible or SMP kernel, your driver can be used
> before the initialization has completed.
>
> As this driver calls sdhci_pltfm_register() before it has obtained the
> clock for the interface, and this function does:
> sdhci_pltfm_init
> sdhci_add_host
> mmc_add_host
> mmc_start_host
> mmc_power_up
> mmc_set_ios
> sdhci_set_ios
>
> See, we're trying to power up and clock the card _before_ the dove
> sdhci driver has even claimed the clock let alone enabled it. This
> is total bollocks. The sdhci platform interface is total crap for
> creating this broken design in the first place. This is why MMC has
> the init + add interfaces, they're there to allow drivers to do stuff
> the Right(tm) way and avoid shit like the above.
>
> This should have been picked up at review time before the driver went
> into mainline. In any case, it needs to be fixed.

Here's an updated patch which just about fixes the sdhci-dove driver.
I would not be surprised given the idiotic sdhci-pltfm API if many
other drivers suffered the same bug.

8<====
From: Russell King <rmk+kernel@arm.linux.org.uk>
Subject: [PATCH] MMC: fix sdhci-dove probe/removal

1. Never ever publish a device in the system before it has been setup
to a usable state.
2. Unregister the device _BEFORE_ taking away any resources it may be
using.
3. Don't check clks against NULL.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
---
drivers/mmc/host/sdhci-dove.c | 36 ++++++++++++++++++------------------
1 files changed, 18 insertions(+), 18 deletions(-)

diff --git a/drivers/mmc/host/sdhci-dove.c b/drivers/mmc/host/sdhci-dove.c
index a6e53a1..7d3a4e4 100644
--- a/drivers/mmc/host/sdhci-dove.c
+++ b/drivers/mmc/host/sdhci-dove.c
@@ -83,30 +83,31 @@ static int __devinit sdhci_dove_probe(struct platform_device *pdev)
struct sdhci_dove_priv *priv;
int ret;

- ret = sdhci_pltfm_register(pdev, &sdhci_dove_pdata);
- if (ret)
- goto sdhci_dove_register_fail;
-
priv = devm_kzalloc(&pdev->dev, sizeof(struct sdhci_dove_priv),
GFP_KERNEL);
if (!priv) {
dev_err(&pdev->dev, "unable to allocate private data");
- ret = -ENOMEM;
- goto sdhci_dove_allocate_fail;
+ return -ENOMEM;
}

+ priv->clk = clk_get(&pdev->dev, NULL);
+ if (!IS_ERR(priv->clk))
+ clk_prepare_enable(priv->clk);
+
+ ret = sdhci_pltfm_register(pdev, &sdhci_dove_pdata);
+ if (ret)
+ goto sdhci_dove_register_fail;
+
host = platform_get_drvdata(pdev);
pltfm_host = sdhci_priv(host);
pltfm_host->priv = priv;

- priv->clk = clk_get(&pdev->dev, NULL);
- if (!IS_ERR(priv->clk))
- clk_prepare_enable(priv->clk);
return 0;

-sdhci_dove_allocate_fail:
- sdhci_pltfm_unregister(pdev);
sdhci_dove_register_fail:
+ clk_unprepare_disable(priv->clk);
+ clk_put(priv->clk);
+sdhci_dove_allocate_fail:
return ret;
}

@@ -116,14 +117,13 @@ static int __devexit sdhci_dove_remove(struct platform_device *pdev)
struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
struct sdhci_dove_priv *priv = pltfm_host->priv;

- if (priv->clk) {
- if (!IS_ERR(priv->clk)) {
- clk_disable_unprepare(priv->clk);
- clk_put(priv->clk);
- }
- devm_kfree(&pdev->dev, priv->clk);
+ sdhci_pltfm_unregister(pdev);
+
+ if (!IS_ERR(priv->clk)) {
+ clk_disable_unprepare(priv->clk);
+ clk_put(priv->clk);
}
- return sdhci_pltfm_unregister(pdev);
+ return 0;
}

static struct platform_driver sdhci_dove_driver = {
--
1.7.4.4