* Re: drivers binding to device node with multiple compatible strings
2018-09-28 21:00 ` Li Yang
@ 2018-09-28 21:19 ` Li Yang
2018-10-02 14:19 ` Rob Herring
2018-10-04 9:32 ` Grant Likely
2 siblings, 0 replies; 9+ messages in thread
From: Li Yang @ 2018-09-28 21:19 UTC (permalink / raw)
To: Rob Herring
Cc: Grant Likely,
open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS, lkml,
moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE,
linuxppc-dev, frowand.list
On Fri, Sep 28, 2018 at 4:00 PM Li Yang <leoyang.li@nxp.com> wrote:
>
> On Fri, Sep 28, 2018 at 3:07 PM Rob Herring <robh+dt@kernel.org> wrote:
> >
> > On Thu, Sep 27, 2018 at 5:25 PM Li Yang <leoyang.li@nxp.com> wrote:
> > >
> > > Hi Rob and Grant,
> > >
> > > Various device tree specs are recommending to include all the
> > > potential compatible strings in the device node, with the order from
> > > most specific to most general. But it looks like Linux kernel doesn't
> > > provide a way to bind the device to the most specific driver, however,
> > > the first registered compatible driver will be bound.
> > >
> > > As more and more generic drivers are added to the Linux kernel, they
> > > are competing with the more specific vendor drivers and causes problem
> > > when both are built into the kernel. I'm wondering if there is a
> > > generic solution (or in plan) to make the most specific driver bound
> > > to the device. Or we have to disable the more general driver or
> > > remove the more general compatible string from the device tree?
> >
> > It's been a known limitation for a long time. However, in practice it
> > doesn't seem to be a common problem. Perhaps folks just remove the
> > less specific compatible from their DT (though that's not ideal). For
> > most modern bindings, there's so many other resources beyond
> > compatible (clocks, resets, pinctrl, etc.) that there are few generic
> > drivers that can work.
> >
> > I guess if we want to fix this, we'd need to have weighted matching in
> > the driver core and unbind drivers when we get a better match. Though
> > it could get messy if the better driver probe fails. Then we've got to
> > rebind to the original driver.
>
> Probably we can populate the platform devices from device tree after
> the device_init phase? So that all built-in drivers are already
> registered when the devices are created and we can try find the best
> match in one go? For more specific loadable modules we probably need
> to unbind from the old driver and bind to the new one. But I agree
> with you that it could be messy.
>
> >
> > Do you have a specific case where you hit this?
>
> Maybe not a new issue but "snps,dw-pcie" is competing with various
> "fsl,<chip>-pcie" compatibles. Also a specific PHY
> "ethernet-phy-idAAAA.BBBB" with generic "ethernet-phy-ieee802.3-c45".
The ethernet-phy issue is not related to the general device binding
framework, it should be an issue with the of_mdio framework. But it is
still a inalignment with the device tree recommendation.
Regards,
Leo
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: drivers binding to device node with multiple compatible strings
2018-09-28 21:00 ` Li Yang
2018-09-28 21:19 ` Li Yang
@ 2018-10-02 14:19 ` Rob Herring
2018-10-04 9:32 ` Grant Likely
2 siblings, 0 replies; 9+ messages in thread
From: Rob Herring @ 2018-10-02 14:19 UTC (permalink / raw)
To: Yang-Leo Li
Cc: Grant Likely, devicetree, linux-kernel,
moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE,
linuxppc-dev, Frank Rowand
On Fri, Sep 28, 2018 at 4:01 PM Li Yang <leoyang.li@nxp.com> wrote:
>
> On Fri, Sep 28, 2018 at 3:07 PM Rob Herring <robh+dt@kernel.org> wrote:
> >
> > On Thu, Sep 27, 2018 at 5:25 PM Li Yang <leoyang.li@nxp.com> wrote:
> > >
> > > Hi Rob and Grant,
> > >
> > > Various device tree specs are recommending to include all the
> > > potential compatible strings in the device node, with the order from
> > > most specific to most general. But it looks like Linux kernel doesn't
> > > provide a way to bind the device to the most specific driver, however,
> > > the first registered compatible driver will be bound.
> > >
> > > As more and more generic drivers are added to the Linux kernel, they
> > > are competing with the more specific vendor drivers and causes problem
> > > when both are built into the kernel. I'm wondering if there is a
> > > generic solution (or in plan) to make the most specific driver bound
> > > to the device. Or we have to disable the more general driver or
> > > remove the more general compatible string from the device tree?
> >
> > It's been a known limitation for a long time. However, in practice it
> > doesn't seem to be a common problem. Perhaps folks just remove the
> > less specific compatible from their DT (though that's not ideal). For
> > most modern bindings, there's so many other resources beyond
> > compatible (clocks, resets, pinctrl, etc.) that there are few generic
> > drivers that can work.
> >
> > I guess if we want to fix this, we'd need to have weighted matching in
> > the driver core and unbind drivers when we get a better match. Though
> > it could get messy if the better driver probe fails. Then we've got to
> > rebind to the original driver.
>
> Probably we can populate the platform devices from device tree after
> the device_init phase? So that all built-in drivers are already
> registered when the devices are created and we can try find the best
> match in one go? For more specific loadable modules we probably need
> to unbind from the old driver and bind to the new one. But I agree
> with you that it could be messy.
>
> >
> > Do you have a specific case where you hit this?
>
> Maybe not a new issue but "snps,dw-pcie" is competing with various
> "fsl,<chip>-pcie" compatibles.
Having "snps,dw-pcie" is pretty useless IMO. There's lots of versions
of the IP and variations on how it is integrated by various SoC
vendors.
> Also a specific PHY
> "ethernet-phy-idAAAA.BBBB" with generic "ethernet-phy-ieee802.3-c45".
MDIO device probing works a bit differently, so I don't think there's
a problem there. Drivers for specific phys should have a
.match_phy_device() callback. I could be wrong as I'm not all that
familiar with the MDIO bus code.
Rob
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: drivers binding to device node with multiple compatible strings
2018-09-28 21:00 ` Li Yang
2018-09-28 21:19 ` Li Yang
2018-10-02 14:19 ` Rob Herring
@ 2018-10-04 9:32 ` Grant Likely
2018-10-04 9:39 ` Grant Likely
2 siblings, 1 reply; 9+ messages in thread
From: Grant Likely @ 2018-10-04 9:32 UTC (permalink / raw)
To: leoyang.li
Cc: Rob Herring,
open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS,
Linux Kernel Mailing List, Linux ARM, linuxppc-dev, Frank Rowand,
Grant Likely
On Fri, Sep 28, 2018 at 10:01 PM Li Yang <leoyang.li@nxp.com> wrote:
>
> On Fri, Sep 28, 2018 at 3:07 PM Rob Herring <robh+dt@kernel.org> wrote:
> >
> > On Thu, Sep 27, 2018 at 5:25 PM Li Yang <leoyang.li@nxp.com> wrote:
> > >
> > > Hi Rob and Grant,
> > >
> > > Various device tree specs are recommending to include all the
> > > potential compatible strings in the device node, with the order from
> > > most specific to most general. But it looks like Linux kernel doesn't
> > > provide a way to bind the device to the most specific driver, however,
> > > the first registered compatible driver will be bound.
> > >
> > > As more and more generic drivers are added to the Linux kernel, they
> > > are competing with the more specific vendor drivers and causes problem
> > > when both are built into the kernel. I'm wondering if there is a
> > > generic solution (or in plan) to make the most specific driver bound
> > > to the device. Or we have to disable the more general driver or
> > > remove the more general compatible string from the device tree?
> >
> > It's been a known limitation for a long time. However, in practice it
> > doesn't seem to be a common problem. Perhaps folks just remove the
> > less specific compatible from their DT (though that's not ideal). For
> > most modern bindings, there's so many other resources beyond
> > compatible (clocks, resets, pinctrl, etc.) that there are few generic
> > drivers that can work.
> >
> > I guess if we want to fix this, we'd need to have weighted matching in
> > the driver core and unbind drivers when we get a better match. Though
> > it could get messy if the better driver probe fails. Then we've got to
> > rebind to the original driver.
>
> Probably we can populate the platform devices from device tree after
> the device_init phase? So that all built-in drivers are already
> registered when the devices are created and we can try find the best
> match in one go? For more specific loadable modules we probably need
> to unbind from the old driver and bind to the new one. But I agree
> with you that it could be messy.
It's a tradeoff.
>
> >
> > Do you have a specific case where you hit this?
>
> Maybe not a new issue but "snps,dw-pcie" is competing with various
> "fsl,<chip>-pcie" compatibles. Also a specific PHY
> "ethernet-phy-idAAAA.BBBB" with generic "ethernet-phy-ieee802.3-c45".
>
> Regards,
> Leo
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: drivers binding to device node with multiple compatible strings
2018-10-04 9:32 ` Grant Likely
@ 2018-10-04 9:39 ` Grant Likely
0 siblings, 0 replies; 9+ messages in thread
From: Grant Likely @ 2018-10-04 9:39 UTC (permalink / raw)
To: Grant Likely, leoyang.li
Cc: nd, Rob Herring,
open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS,
Linux Kernel Mailing List, Linux ARM, linuxppc-dev, Frank Rowand
On 04/10/2018 10:32, Grant Likely wrote:
> On Fri, Sep 28, 2018 at 10:01 PM Li Yang <leoyang.li@nxp.com> wrote:
>>
>> On Fri, Sep 28, 2018 at 3:07 PM Rob Herring <robh+dt@kernel.org> wrote:
>>>
>>> On Thu, Sep 27, 2018 at 5:25 PM Li Yang <leoyang.li@nxp.com> wrote:
>>>>
>>>> Hi Rob and Grant,
>>>>
>>>> Various device tree specs are recommending to include all the
>>>> potential compatible strings in the device node, with the order from
>>>> most specific to most general. But it looks like Linux kernel doesn't
>>>> provide a way to bind the device to the most specific driver, however,
>>>> the first registered compatible driver will be bound.
>>>>
>>>> As more and more generic drivers are added to the Linux kernel, they
>>>> are competing with the more specific vendor drivers and causes problem
>>>> when both are built into the kernel. I'm wondering if there is a
>>>> generic solution (or in plan) to make the most specific driver bound
>>>> to the device. Or we have to disable the more general driver or
>>>> remove the more general compatible string from the device tree?
>>>
>>> It's been a known limitation for a long time. However, in practice it
>>> doesn't seem to be a common problem. Perhaps folks just remove the
>>> less specific compatible from their DT (though that's not ideal). For
>>> most modern bindings, there's so many other resources beyond
>>> compatible (clocks, resets, pinctrl, etc.) that there are few generic
>>> drivers that can work.
>>>
>>> I guess if we want to fix this, we'd need to have weighted matching in
>>> the driver core and unbind drivers when we get a better match. Though
>>> it could get messy if the better driver probe fails. Then we've got to
>>> rebind to the original driver.
>>
>> Probably we can populate the platform devices from device tree after
>> the device_init phase? So that all built-in drivers are already
>> registered when the devices are created and we can try find the best
>> match in one go? For more specific loadable modules we probably need
>> to unbind from the old driver and bind to the new one. But I agree
>> with you that it could be messy.
>
> It's a tradeoff.
Oops! Accidentally hit send too early.
It's a tradeoff. If the platform device population is deferred until
after all drivers are loaded, then there isn't any mechanism to ensure
some devices get probed early in the init sequence.
As Rob said, while it is a problem in theory, there haven't been a lot
of actual cases where it is a problem. The solution has been to either
remove the generic match from the device, or we can blacklist particular
devices from the generic driver.
g.
>>
>>>
>>> Do you have a specific case where you hit this?
>>
>> Maybe not a new issue but "snps,dw-pcie" is competing with various
>> "fsl,<chip>-pcie" compatibles. Also a specific PHY
>> "ethernet-phy-idAAAA.BBBB" with generic "ethernet-phy-ieee802.3-c45".
>>
>> Regards,
>> Leo
^ permalink raw reply [flat|nested] 9+ messages in thread