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A resizable BAR is different from a normal BAR in a few ways:
- The minimum size of a resizable BAR is 1 MB.
- Each BAR that is resizable has a Capability and Control register in
the Resizable BAR Capability structure.
These registers contain the supported sizes and the currently selected
size of a resizable BAR.
The supported sizes is a bitmap of the supported sizes. The selected size
is a single value that is equal to one of the supported sizes.
A resizable BAR thus has to be configured differently than a
BAR_PROGRAMMABLE BAR, which usually sets the BAR size/mask in a vendor
specific way.
The PCI endpoint framework currently does not support resizable BARs.
Add a BAR type BAR_RESIZABLE, so that an EPC driver can support resizable
BARs properly.
Note that the pci_epc_set_bar() API takes a struct pci_epf_bar which tells
the EPC driver how it wants to configure the BAR.
struct pci_epf_bar only has a single size struct member.
This means that an EPC driver will only be able to set a single supported
size. This is perfectly fine, as we do not need the complexity of allowing
a host to change the size of the BAR. If someone ever wants to support
resizing a resizable BAR, the pci_epc_set_bar() API can be extended in the
future.
With these changes, we allow an EPF driver to configure the size of
Resizable BARs, rather than forcing them to a 1 MB size.
Signed-off-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20250131182949.465530-10-cassel@kernel.org
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
[kwilczynski: commit log]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.