imx6 eSATA

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Sat, Jan 18, 2014 at 07:03:37PM +0000, Russell King - ARM Linux wrote:
> On Sat, Jan 18, 2014 at 06:44:27PM +0000, Russell King - ARM Linux wrote:
> > So, I see we have AHCI support for SATA on the iMX6.  Great... but it
> > doesn't work on the cubox-i, because the phy settings are wrong.
> 
> And another thing.  This is wonderful... really wonderful.
> 
> static int imx_ahci_probe(struct platform_device *pdev)
> {  
>         struct device *dev = &pdev->dev;
> ...
>         ahci_pdev = platform_device_alloc("ahci", -1);
> ...
>         ahci_dev = &ahci_pdev->dev; 
> ...
>         ahci_dev->of_node = dev->of_node;
> 
> This is a hanging offence.
> 
> Here's a lesson in how DT matching works:
> 
> - A device gets declared into the device model.
> - The device is offered to each driver in turn via the bus specific
>   code to see whether the driver should be bound to the device.
> - If there's an of_node present, the DT IDs for the driver are walked
>   to compare the device with the driver's DT IDs.  If a match is found,
>   the device is passed to the driver probe function.
> - If there is no of_node present, and it's a platform device, the bare
>   device name is compared the driver name(s) and if it matches the
>   probe function is called.
> 
> Now, what does this mean for the above monstrosity?  If the driver
> model happens to find the ahci_imx driver _before_ the ahci driver
> while trying to bind the ahci_dev, it will find that the ahci_dev
> has an of_node with a compatible string which matches this driver.
> So, imx_ahci_probe() _can_ be called with the ahci_pdev that it
> just created.
> 
> It doesn't take much to understand what the result will be of that.
> It will try to create another ahci device... hopefully this time
> erroring out.
> 
> This is utterly disgusting.  You must *never* *ever* assign an of_node
> from one device to another of the same bus type.  If you need to pass
> the of_node to another device, then it _must_ be done outside of the
> child device's of_node pointer - in other words, it must be done using
> platform data.
> 
> Alternatively, turn ahci into a library that both the original ahci
> and ahci_imx drivers can use without jumping through these kinds of
> games - or in this case, just get rid of that assignment - I can't
> see anything in ahci.c which needs the of_node.

Sigh.  You can't get rid of the of_node there because it's needed
for clk_get() inside ahci_platform.c.  So, I think ahci_platform needs
to become yet another library, and thereby avoid creating a child
platform device.

-- 
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