spi: microchip-core-qspi: Add regular transfers

Merge series from Conor Dooley <conor@kernel.org>:

This is a v2 of a patchset I sent about this time last year, adding the
regular transfer_one_message op to the microchip-core-qspi driver. In that
v1 Mark expressed his dislike for that op, so v2 is using
prepare/unprepare/transfer_one instead. The unprepare implementation still
contains the 750 us delay that the driver had back in v1. I've heard a
suggestion internally as to why this is needed, but it was unsubstantiated,
so I still have no justification for it. I held off on sending a v2 because
of a lack of explanation for the delay, but I don't wanna hold off forever
for something I might never understand.

1 files changed, 40 insertions, 0 deletions

diff --git a/mm/util.c b/mm/util.c
index 448117da071f..0b270c43d7d1 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -1131,3 +1131,43 @@ void flush_dcache_folio(struct folio *folio)
 }
 EXPORT_SYMBOL(flush_dcache_folio);
 #endif
+
+/**
+ * compat_vma_mmap_prepare() - Apply the file's .mmap_prepare() hook to an
+ * existing VMA
+ * @file: The file which possesss an f_op->mmap_prepare() hook
+ * @vma: The VMA to apply the .mmap_prepare() hook to.
+ *
+ * Ordinarily, .mmap_prepare() is invoked directly upon mmap(). However, certain
+ * 'wrapper' file systems invoke a nested mmap hook of an underlying file.
+ *
+ * Until all filesystems are converted to use .mmap_prepare(), we must be
+ * conservative and continue to invoke these 'wrapper' filesystems using the
+ * deprecated .mmap() hook.
+ *
+ * However we have a problem if the underlying file system possesses an
+ * .mmap_prepare() hook, as we are in a different context when we invoke the
+ * .mmap() hook, already having a VMA to deal with.
+ *
+ * compat_vma_mmap_prepare() is a compatibility function that takes VMA state,
+ * establishes a struct vm_area_desc descriptor, passes to the underlying
+ * .mmap_prepare() hook and applies any changes performed by it.
+ *
+ * Once the conversion of filesystems is complete this function will no longer
+ * be required and will be removed.
+ *
+ * Returns: 0 on success or error.
+ */
+int compat_vma_mmap_prepare(struct file *file, struct vm_area_struct *vma)
+{
+	struct vm_area_desc desc;
+	int err;
+
+	err = file->f_op->mmap_prepare(vma_to_desc(vma, &desc));
+	if (err)
+		return err;
+	set_vma_from_desc(vma, &desc);
+
+	return 0;
+}
+EXPORT_SYMBOL(compat_vma_mmap_prepare);