[PATCH] docs: driver-api: firmware: add driver firmware guidelines. (v2)
From: Dave Airlie airlied@redhat.com
A recent snafu where Intel ignored upstream feedback on a firmware change, led to a late rc6 fix being required. In order to avoid this in the future we should document some expectations around linux-firmware.
I was originally going to write this for drm, but it seems quite generic advice.
v2: rewritten with suggestions from Thorsten Leemhuis.
Acked-by: Luis Chamberlain mcgrof@kernel.org Acked-by: Rodrigo Vivi rodrigo.vivi@intel.com Signed-off-by: Dave Airlie airlied@redhat.com --- Documentation/driver-api/firmware/core.rst | 1 + .../firmware/firmware-usage-guidelines.rst | 34 +++++++++++++++++++ 2 files changed, 35 insertions(+) create mode 100644 Documentation/driver-api/firmware/firmware-usage-guidelines.rst
diff --git a/Documentation/driver-api/firmware/core.rst b/Documentation/driver-api/firmware/core.rst index 1d1688cbc078..803cd574bbd7 100644 --- a/Documentation/driver-api/firmware/core.rst +++ b/Documentation/driver-api/firmware/core.rst @@ -13,4 +13,5 @@ documents these features. direct-fs-lookup fallback-mechanisms lookup-order + firmware-usage-guidelines
diff --git a/Documentation/driver-api/firmware/firmware-usage-guidelines.rst b/Documentation/driver-api/firmware/firmware-usage-guidelines.rst new file mode 100644 index 000000000000..34d2412e78c6 --- /dev/null +++ b/Documentation/driver-api/firmware/firmware-usage-guidelines.rst @@ -0,0 +1,34 @@ +=================== +Firmware Guidelines +=================== + +Drivers that use firmware from linux-firmware should attempt to follow +the rules in this guide. + +* Firmware should be versioned with at least a major/minor version. It + is suggested that the firmware files in linux-firmware be named with + some device specific name, and just the major version. The + major/minor/patch versions should be stored in a header in the + firmware file for the driver to detect any non-ABI fixes/issues. The + firmware files in linux-firmware should be overwritten with the newest + compatible major version. Newer major version firmware should remain + compatible with all kernels that load that major number. + +* Users should *not* have to install newer firmware to use existing + hardware when they install a newer kernel. If the hardware isn't + enabled by default or under development, this can be ignored, until + the first kernel release that enables that hardware. This means no + major version bumps without the kernel retaining backwards + compatibility for the older major versions. Minor version bumps + should not introduce new features that newer kernels depend on + non-optionally. + +* If a security fix needs lockstep firmware and kernel fixes in order to + be successful, then all supported major versions in the linux-firmware + repo should be updated with the security fix, and the kernel patches + should detect if the firmware is new enough to declare if the security + issue is fixed. All communications around security fixes should point + at both the firmware and kernel fixes. If a security fix requires + deprecating old major versions, then this should only be done as a + last option, and be stated clearly in all communications. +
Em Tue, 19 Jul 2022 16:53:57 +1000 Dave Airlie airlied@gmail.com escreveu:
From: Dave Airlie airlied@redhat.com
A recent snafu where Intel ignored upstream feedback on a firmware change, led to a late rc6 fix being required. In order to avoid this in the future we should document some expectations around linux-firmware.
I was originally going to write this for drm, but it seems quite generic advice.
Indeed it makes sense to document firmware API compatibility in a generic way.
Some suggestions below.
v2: rewritten with suggestions from Thorsten Leemhuis.
Acked-by: Luis Chamberlain mcgrof@kernel.org Acked-by: Rodrigo Vivi rodrigo.vivi@intel.com Signed-off-by: Dave Airlie airlied@redhat.com
Documentation/driver-api/firmware/core.rst | 1 + .../firmware/firmware-usage-guidelines.rst | 34 +++++++++++++++++++ 2 files changed, 35 insertions(+) create mode 100644 Documentation/driver-api/firmware/firmware-usage-guidelines.rst
diff --git a/Documentation/driver-api/firmware/core.rst b/Documentation/driver-api/firmware/core.rst index 1d1688cbc078..803cd574bbd7 100644 --- a/Documentation/driver-api/firmware/core.rst +++ b/Documentation/driver-api/firmware/core.rst @@ -13,4 +13,5 @@ documents these features. direct-fs-lookup fallback-mechanisms lookup-order
- firmware-usage-guidelines
diff --git a/Documentation/driver-api/firmware/firmware-usage-guidelines.rst b/Documentation/driver-api/firmware/firmware-usage-guidelines.rst new file mode 100644 index 000000000000..34d2412e78c6 --- /dev/null +++ b/Documentation/driver-api/firmware/firmware-usage-guidelines.rst @@ -0,0 +1,34 @@ +=================== +Firmware Guidelines +===================
+Drivers that use firmware from linux-firmware should attempt to follow +the rules in this guide.
+* Firmware should be versioned with at least a major/minor version.
It is hard to enforce how vendors will version their firmware. On media, we have some drivers whose major means different hardware versions. For instance, on xc3028, v3.x means low voltage chips, while v2.x means "normal" voltage. We end changing the file name on Linux to avoid the risk of damaging the hardware, as using v27 firmware on low power chips damage them. So, we have:
drivers/media/tuners/xc2028.h:#define XC2028_DEFAULT_FIRMWARE "xc3028-v27.fw" drivers/media/tuners/xc2028.h:#define XC3028L_DEFAULT_FIRMWARE "xc3028L-v36.fw"
As their main market is not Linux - nor PC - as their main sales are on TV sets, and them don't officially support Linux, there's nothing we can do to enforce it.
IMO we need a more generic text here to indicate that Linux firmware files should be defined in a way that it should be possible to detect when there are incompatibilities with past versions. So, I would say, instead:
Firmware files shall be designed in a way that it allows checking for firmware ABI version changes. It is recommended that firmware files to be versioned with at least major/minor version.
It
- is suggested that the firmware files in linux-firmware be named with
- some device specific name, and just the major version.
The
- major/minor/patch versions should be stored in a header in the
- firmware file for the driver to detect any non-ABI fixes/issues.
I would also make this more generic. On media, we ended adding the firmware version indicated at the file name. For instance, xc4000 driver checks for two firmware files:
drivers/media/tuners/xc4000.c:#define XC4000_DEFAULT_FIRMWARE "dvb-fe-xc4000-1.4.fw" drivers/media/tuners/xc4000.c:#define XC4000_DEFAULT_FIRMWARE_NEW "dvb-fe-xc4000-1.4.1.fw"
On such cases, the driver can take decisions based on the firmware name.
I would change the text to be more generic covering both cases:
The firmware version shall either be stored at the firmware header or as part of the firmware file name, in order to let the driver to detect any non-ABI fixes/changes.
The
- firmware files in linux-firmware should be overwritten with the newest
- compatible major version.
For me "shall" is mandatory, while "should" is optional.
In this specific case, I'm not so sure if overriding it is the best thing to do on all subsystems. I mean, even with the same ABI, older firmware usually means that some bugs and/or limitations will be present there.
That's specially true on codecs: even having the same ABI, older versions won't support decoding newer protocols. We have one case with some digital TV decoders that only support some Cable-TV protocols with newer firmware versions. We have also one case were remote controller decoding is buggy with older firmwares. On both situations, the ABI didn't change.
Newer major version firmware should remain
- compatible with all kernels that load that major number.
should -> shall
+* Users should *not* have to install newer firmware to use existing
- hardware when they install a newer kernel.
If the hardware isn't
- enabled by default or under development,
Hmm.. someone might understand that not having a "default Y" at Kconfig would mean that this is not enabled by default ;-)
IMO you can just tell, instead:
"This can be ignored until the first kernel release that enables support for such hardware."
this can be ignored, until
- the first kernel release that enables that hardware.
This means no
- major version bumps without the kernel retaining backwards
- compatibility for the older major versions. Minor version bumps
- should not introduce new features that newer kernels depend on
- non-optionally.
+* If a security fix needs lockstep firmware and kernel fixes in order to
- be successful, then all supported major versions in the linux-firmware
- repo should be updated with the security fix, and the kernel patches
- should detect if the firmware is new enough to declare if the security
- issue is fixed. All communications around security fixes should point
- at both the firmware and kernel fixes. If a security fix requires
- deprecating old major versions, then this should only be done as a
- last option, and be stated clearly in all communications.
Perfect!
Regards, Mauro
It is hard to enforce how vendors will version their firmware. On media, we have some drivers whose major means different hardware versions. For instance, on xc3028, v3.x means low voltage chips, while v2.x means "normal" voltage. We end changing the file name on Linux to avoid the risk of damaging the hardware, as using v27 firmware on low power chips damage them. So, we have:
drivers/media/tuners/xc2028.h:#define XC2028_DEFAULT_FIRMWARE "xc3028-v27.fw" drivers/media/tuners/xc2028.h:#define XC3028L_DEFAULT_FIRMWARE "xc3028L-v36.fw"As their main market is not Linux - nor PC - as their main sales are on TV sets, and them don't officially support Linux, there's nothing we can do to enforce it.
IMO we need a more generic text here to indicate that Linux firmware files should be defined in a way that it should be possible to detect when there are incompatibilities with past versions. So, I would say, instead:
Firmware files shall be designed in a way that it allows checking for firmware ABI version changes. It is recommended that firmware files to be versioned with at least major/minor version.
This sounds good, will update with this.
It
- is suggested that the firmware files in linux-firmware be named with
- some device specific name, and just the major version.
The
- major/minor/patch versions should be stored in a header in the
- firmware file for the driver to detect any non-ABI fixes/issues.
I would also make this more generic. On media, we ended adding the firmware version indicated at the file name. For instance, xc4000 driver checks for two firmware files:
drivers/media/tuners/xc4000.c:#define XC4000_DEFAULT_FIRMWARE "dvb-fe-xc4000-1.4.fw" drivers/media/tuners/xc4000.c:#define XC4000_DEFAULT_FIRMWARE_NEW "dvb-fe-xc4000-1.4.1.fw"
This is probably fine for products where development never produces much firmwares, but it quickly becomes unmanageable when you end up with _NEW_NEW_NEW etc.
I'd rather not encourage this sort of thing unless it is totally outside our control. So I'd like to keep the guidelines for when we have some control what we'd recommend.
In this case I'd have recommended you put the 1.4.1 in the header of the fw, and just have it called dvb-fe-xc4000-1.fw and overwrite the NEW with the OLD, I understand we likely don't have the control here.
- firmware files in linux-firmware should be overwritten with the newest
- compatible major version.
For me "shall" is mandatory, while "should" is optional.
In this specific case, I'm not so sure if overriding it is the best thing to do on all subsystems. I mean, even with the same ABI, older firmware usually means that some bugs and/or limitations will be present there.
As long as you can detect the minor/patch versions from the firmware file after loading it you should be able to do sufficient workarounds.
That's specially true on codecs: even having the same ABI, older versions won't support decoding newer protocols. We have one case with some digital TV decoders that only support some Cable-TV protocols with newer firmware versions. We have also one case were remote controller decoding is buggy with older firmwares. On both situations, the ABI didn't change.
If the only way to figure that out is by the filename or minor version, then so be it, but where people have some control I'd rather provide some harder guidelines.
Dave.
On 2022-07-19 02:53, Dave Airlie wrote:
From: Dave Airlie airlied@redhat.com
A recent snafu where Intel ignored upstream feedback on a firmware change, led to a late rc6 fix being required. In order to avoid this in the future we should document some expectations around linux-firmware.
I was originally going to write this for drm, but it seems quite generic advice.
v2: rewritten with suggestions from Thorsten Leemhuis.
Acked-by: Luis Chamberlain mcgrof@kernel.org Acked-by: Rodrigo Vivi rodrigo.vivi@intel.com
Acked-by: Harry Wentland harry.wentland@amd.com
Harry
Signed-off-by: Dave Airlie airlied@redhat.com
Documentation/driver-api/firmware/core.rst | 1 + .../firmware/firmware-usage-guidelines.rst | 34 +++++++++++++++++++ 2 files changed, 35 insertions(+) create mode 100644 Documentation/driver-api/firmware/firmware-usage-guidelines.rst
diff --git a/Documentation/driver-api/firmware/core.rst b/Documentation/driver-api/firmware/core.rst index 1d1688cbc078..803cd574bbd7 100644 --- a/Documentation/driver-api/firmware/core.rst +++ b/Documentation/driver-api/firmware/core.rst @@ -13,4 +13,5 @@ documents these features. direct-fs-lookup fallback-mechanisms lookup-order
- firmware-usage-guidelines
diff --git a/Documentation/driver-api/firmware/firmware-usage-guidelines.rst b/Documentation/driver-api/firmware/firmware-usage-guidelines.rst new file mode 100644 index 000000000000..34d2412e78c6 --- /dev/null +++ b/Documentation/driver-api/firmware/firmware-usage-guidelines.rst @@ -0,0 +1,34 @@ +=================== +Firmware Guidelines +===================
+Drivers that use firmware from linux-firmware should attempt to follow +the rules in this guide.
+* Firmware should be versioned with at least a major/minor version. It
- is suggested that the firmware files in linux-firmware be named with
- some device specific name, and just the major version. The
- major/minor/patch versions should be stored in a header in the
- firmware file for the driver to detect any non-ABI fixes/issues. The
- firmware files in linux-firmware should be overwritten with the newest
- compatible major version. Newer major version firmware should remain
- compatible with all kernels that load that major number.
+* Users should *not* have to install newer firmware to use existing
- hardware when they install a newer kernel. If the hardware isn't
- enabled by default or under development, this can be ignored, until
- the first kernel release that enables that hardware. This means no
- major version bumps without the kernel retaining backwards
- compatibility for the older major versions. Minor version bumps
- should not introduce new features that newer kernels depend on
- non-optionally.
+* If a security fix needs lockstep firmware and kernel fixes in order to
- be successful, then all supported major versions in the linux-firmware
- repo should be updated with the security fix, and the kernel patches
- should detect if the firmware is new enough to declare if the security
- issue is fixed. All communications around security fixes should point
- at both the firmware and kernel fixes. If a security fix requires
- deprecating old major versions, then this should only be done as a
- last option, and be stated clearly in all communications.
participants (3)
-
Dave Airlie -
Harry Wentland -
Mauro Carvalho Chehab