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Revision 6af8ae321a801a4e20183454c65eb0d23069d8ac authored by Phil Elwell on 28 January 2021, 11:30:04 UTC, committed by Phil Elwell on 28 January 2021, 11:46:41 UTC 
spi: bcm2835: Workaround/fix for zero-length transfers
 
A relatively recent commit ([1]) contained optimisation for the PIO
SPI FIFO-filling functions. The commit message includes the phrase
"[t]he blind and counted loops are always called with nonzero count".
This is technically true, but it is still possible for count to become
zero before the loop is entered - if tfr->len is zero. Moving the loop
exit condition to the end of the loop saves a few cycles, but results
in a near-infinite loop should the revised count be zero on entry.

Strangely, zero-lengthed transfers aren't filtered by the SPI framework
and, even more strangely, the Python3 spidev library is triggering them
for no obvious reason.

Avoid the problem completely by bailing out of the main transfer
function early if trf->len is zero, although there may be a case for
moving the mitigation into the framework.

See: https://github.com/raspberrypi/linux/issues/4100

Signed-off-by: Phil Elwell <phil@raspberrypi.com>

[1] 26751de25d25 ("spi: bcm2835: Micro-optimise FIFO loops")
1 parent c5f51df
Raw File
mmzone.c 
// SPDX-License-Identifier: GPL-2.0
/*
 * linux/mm/mmzone.c
 *
 * management codes for pgdats, zones and page flags
 */


#include <linux/stddef.h>
#include <linux/mm.h>
#include <linux/mmzone.h>

struct pglist_data *first_online_pgdat(void)
{
	return NODE_DATA(first_online_node);
}

struct pglist_data *next_online_pgdat(struct pglist_data *pgdat)
{
	int nid = next_online_node(pgdat->node_id);

	if (nid == MAX_NUMNODES)
		return NULL;
	return NODE_DATA(nid);
}

/*
 * next_zone - helper magic for for_each_zone()
 */
struct zone *next_zone(struct zone *zone)
{
	pg_data_t *pgdat = zone->zone_pgdat;

	if (zone < pgdat->node_zones + MAX_NR_ZONES - 1)
		zone++;
	else {
		pgdat = next_online_pgdat(pgdat);
		if (pgdat)
			zone = pgdat->node_zones;
		else
			zone = NULL;
	}
	return zone;
}

static inline int zref_in_nodemask(struct zoneref *zref, nodemask_t *nodes)
{
#ifdef CONFIG_NUMA
	return node_isset(zonelist_node_idx(zref), *nodes);
#else
	return 1;
#endif /* CONFIG_NUMA */
}

/* Returns the next zone at or below highest_zoneidx in a zonelist */
struct zoneref *__next_zones_zonelist(struct zoneref *z,
					enum zone_type highest_zoneidx,
					nodemask_t *nodes)
{
	/*
	 * Find the next suitable zone to use for the allocation.
	 * Only filter based on nodemask if it's set
	 */
	if (unlikely(nodes == NULL))
		while (zonelist_zone_idx(z) > highest_zoneidx)
			z++;
	else
		while (zonelist_zone_idx(z) > highest_zoneidx ||
				(z->zone && !zref_in_nodemask(z, nodes)))
			z++;

	return z;
}

#ifdef CONFIG_ARCH_HAS_HOLES_MEMORYMODEL
bool memmap_valid_within(unsigned long pfn,
					struct page *page, struct zone *zone)
{
	if (page_to_pfn(page) != pfn)
		return false;

	if (page_zone(page) != zone)
		return false;

	return true;
}
#endif /* CONFIG_ARCH_HAS_HOLES_MEMORYMODEL */

void lruvec_init(struct lruvec *lruvec)
{
	enum lru_list lru;

	memset(lruvec, 0, sizeof(struct lruvec));

	for_each_lru(lru)
		INIT_LIST_HEAD(&lruvec->lists[lru]);
}

#if defined(CONFIG_NUMA_BALANCING) && !defined(LAST_CPUPID_NOT_IN_PAGE_FLAGS)
int page_cpupid_xchg_last(struct page *page, int cpupid)
{
	unsigned long old_flags, flags;
	int last_cpupid;

	do {
		old_flags = flags = page->flags;
		last_cpupid = page_cpupid_last(page);

		flags &= ~(LAST_CPUPID_MASK << LAST_CPUPID_PGSHIFT);
		flags |= (cpupid & LAST_CPUPID_MASK) << LAST_CPUPID_PGSHIFT;
	} while (unlikely(cmpxchg(&page->flags, old_flags, flags) != old_flags));

	return last_cpupid;
}
#endif
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