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The zpci_get_max_write_size() helper is used to determine the maximum
size a PCI store or load can use at a given __iomem address.
For the PCI block store the following restrictions apply:
1. The dst + len must not cross a 4K boundary in the (pseudo-)MMIO space
2. len must not exceed ZPCI_MAX_WRITE_SIZE
3. len must be a multiple of 8 bytes
4. The src address must be double word (8 byte) aligned
5. The dst address must be double word (8 byte) aligned
Otherwise only a normal PCI store which takes its src value from
a register can be used. For these PCI store restriction 1 still applies.
Similarly 1 also applies to PCI loads.
It turns out zpci_max_write_size() instead implements stricter
conditions which prevents PCI block stores from being used where they
can and should be used. In particular instead of conditions 4 and 5 it
wrongly enforces both dst and src to be size aligned. This indirectly
covers condition 1 but also prevents many legal PCI block stores.
On top of the functional shortcomings the zpci_get_max_write_size() is
misnamed as it is used for both read and write size calculations. Rename
it to zpci_get_max_io_size() and implement the listed conditions
explicitly.
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Fixes:
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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 Restructured Text 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.