Re: [PATCH v3 2/3] openrisc: Introduce new utility functions to flush and invalidate caches

From: Stafford Horne
Date: Wed Mar 26 2025 - 13:12:46 EST

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On Mon, Mar 24, 2025 at 01:25:43AM +0530, Sahil Siddiq wrote:
> According to the OpenRISC architecture manual, the dcache and icache may
> not be present. When these caches are present, the invalidate and flush
> registers may be absent. The current implementation does not perform
> checks to verify their presence before utilizing cache registers, or
> invalidating and flushing cache blocks.
>
> Introduce new functions to detect the presence of cache components and
> related special-purpose registers.
>
> There are a few places where a range of addresses have to be flushed or
> invalidated and the implementation is duplicated. Introduce new utility
> functions and macros that generalize this implementation and reduce
> duplication.
>
> Signed-off-by: Sahil Siddiq <sahilcdq@xxxxxxxxx>
> ---
> Changes from v2 -> v3:
> - arch/openrisc/include/asm/cacheflush.h: Declare new functions and macros.
> - arch/openrisc/include/asm/cpuinfo.h: Implement new functions.
> (cpu_cache_is_present):
> 1. The implementation of this function was strewn all over the place in
> the previous versions.
> 2. Fix condition. The condition in the previous version was incorrect.
> (cb_inv_flush_is_implemented): New function.
> - arch/openrisc/kernel/dma.c: Use new functions.
> - arch/openrisc/mm/cache.c:
> (cache_loop): Extend function.
> (local_*_page_*): Use new cache_loop interface.
> (local_*_range_*): Implement new functions.
> - arch/openrisc/mm/init.c: Use new functions.
>
> arch/openrisc/include/asm/cacheflush.h | 17 +++++++++
> arch/openrisc/include/asm/cpuinfo.h | 42 +++++++++++++++++++++
> arch/openrisc/kernel/dma.c | 18 ++-------
> arch/openrisc/mm/cache.c | 52 ++++++++++++++++++++++----
> arch/openrisc/mm/init.c | 5 ++-
> 5 files changed, 110 insertions(+), 24 deletions(-)
>
> diff --git a/arch/openrisc/include/asm/cacheflush.h b/arch/openrisc/include/asm/cacheflush.h
> index 984c331ff5f4..0e60af486ec1 100644
> --- a/arch/openrisc/include/asm/cacheflush.h
> +++ b/arch/openrisc/include/asm/cacheflush.h
> @@ -23,6 +23,9 @@
> */
> extern void local_dcache_page_flush(struct page *page);
> extern void local_icache_page_inv(struct page *page);
> +extern void local_dcache_range_flush(unsigned long start, unsigned long end);
> +extern void local_dcache_range_inv(unsigned long start, unsigned long end);
> +extern void local_icache_range_inv(unsigned long start, unsigned long end);
>
> /*
> * Data cache flushing always happen on the local cpu. Instruction cache
> @@ -38,6 +41,20 @@ extern void local_icache_page_inv(struct page *page);
> extern void smp_icache_page_inv(struct page *page);
> #endif /* CONFIG_SMP */
>
> +/*
> + * Even if the actual block size is larger than L1_CACHE_BYTES, paddr
> + * can be incremented by L1_CACHE_BYTES. When paddr is written to the
> + * invalidate register, the entire cache line encompassing this address
> + * is invalidated. Each subsequent reference to the same cache line will
> + * not affect the invalidation process.
> + */
> +#define local_dcache_block_flush(addr) \
> + local_dcache_range_flush(addr, addr + L1_CACHE_BYTES)
> +#define local_dcache_block_inv(addr) \
> + local_dcache_range_inv(addr, addr + L1_CACHE_BYTES)
> +#define local_icache_block_inv(addr) \
> + local_icache_range_inv(addr, addr + L1_CACHE_BYTES)
> +
> /*
> * Synchronizes caches. Whenever a cpu writes executable code to memory, this
> * should be called to make sure the processor sees the newly written code.
> diff --git a/arch/openrisc/include/asm/cpuinfo.h b/arch/openrisc/include/asm/cpuinfo.h
> index 82f5d4c06314..7839c41152af 100644
> --- a/arch/openrisc/include/asm/cpuinfo.h
> +++ b/arch/openrisc/include/asm/cpuinfo.h
> @@ -15,6 +15,9 @@
> #ifndef __ASM_OPENRISC_CPUINFO_H
> #define __ASM_OPENRISC_CPUINFO_H
>
> +#include <asm/spr.h>
> +#include <asm/spr_defs.h>
> +
> struct cache_desc {
> u32 size;
> u32 sets;
> @@ -34,4 +37,43 @@ struct cpuinfo_or1k {
> extern struct cpuinfo_or1k cpuinfo_or1k[NR_CPUS];
> extern void setup_cpuinfo(void);
>
> +/*
> + * Check if the cache component exists.
> + */
> +static inline bool cpu_cache_is_present(const unsigned int cache_type)
> +{
> + unsigned long upr = mfspr(SPR_UPR);
> +
> + return !!(upr & (SPR_UPR_UP | cache_type));
> +}
> +
> +/*
> + * Check if the cache block flush/invalidate register is implemented for the
> + * cache component.
> + */
> +static inline bool cb_inv_flush_is_implemented(const unsigned int reg,
> + const unsigned int cache_type)
> +{
> + unsigned long cfgr;
> +
> + if (cache_type == SPR_UPR_DCP) {
> + cfgr = mfspr(SPR_DCCFGR);
> + if (reg == SPR_DCBFR)
> + return !!(cfgr & SPR_DCCFGR_CBFRI);
> +
> + if (reg == SPR_DCBIR)
> + return !!(cfgr & SPR_DCCFGR_CBIRI);
> + }
> +
> + /*
> + * The cache block flush register is not implemented for the instruction cache.
> + */
> + if (cache_type == SPR_UPR_ICP) {
> + cfgr = mfspr(SPR_ICCFGR);
> + return !!(cfgr & SPR_ICCFGR_CBIRI);
> + }
> +
> + return false;
> +}

Could these 2 functions move to cache.c?

> #endif /* __ASM_OPENRISC_CPUINFO_H */
> diff --git a/arch/openrisc/kernel/dma.c b/arch/openrisc/kernel/dma.c
> index b3edbb33b621..3a7b5baaa450 100644
> --- a/arch/openrisc/kernel/dma.c
> +++ b/arch/openrisc/kernel/dma.c
> @@ -17,6 +17,7 @@
> #include <linux/pagewalk.h>
>
> #include <asm/cpuinfo.h>
> +#include <asm/cacheflush.h>
> #include <asm/spr_defs.h>
> #include <asm/tlbflush.h>
>
> @@ -24,9 +25,6 @@ static int
> page_set_nocache(pte_t *pte, unsigned long addr,
> unsigned long next, struct mm_walk *walk)
> {
> - unsigned long cl;
> - struct cpuinfo_or1k *cpuinfo = &cpuinfo_or1k[smp_processor_id()];
> -
> pte_val(*pte) |= _PAGE_CI;
>
> /*
> @@ -36,8 +34,7 @@ page_set_nocache(pte_t *pte, unsigned long addr,
> flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
>
> /* Flush page out of dcache */
> - for (cl = __pa(addr); cl < __pa(next); cl += cpuinfo->dcache_block_size)
> - mtspr(SPR_DCBFR, cl);
> + local_dcache_range_flush(__pa(addr), __pa(next));
>
> return 0;
> }
> @@ -98,21 +95,14 @@ void arch_dma_clear_uncached(void *cpu_addr, size_t size)
> void arch_sync_dma_for_device(phys_addr_t addr, size_t size,
> enum dma_data_direction dir)
> {
> - unsigned long cl;
> - struct cpuinfo_or1k *cpuinfo = &cpuinfo_or1k[smp_processor_id()];
> -
> switch (dir) {
> case DMA_TO_DEVICE:
> /* Flush the dcache for the requested range */
> - for (cl = addr; cl < addr + size;
> - cl += cpuinfo->dcache_block_size)
> - mtspr(SPR_DCBFR, cl);
> + local_dcache_range_flush(addr, addr + size);
> break;
> case DMA_FROM_DEVICE:
> /* Invalidate the dcache for the requested range */
> - for (cl = addr; cl < addr + size;
> - cl += cpuinfo->dcache_block_size)
> - mtspr(SPR_DCBIR, cl);
> + local_dcache_range_inv(addr, addr + size);
> break;
> default:
> /*
> diff --git a/arch/openrisc/mm/cache.c b/arch/openrisc/mm/cache.c
> index eb43b73f3855..aca64c5a20b3 100644
> --- a/arch/openrisc/mm/cache.c
> +++ b/arch/openrisc/mm/cache.c
> @@ -14,31 +14,67 @@
> #include <asm/spr_defs.h>
> #include <asm/cache.h>
> #include <asm/cacheflush.h>
> +#include <asm/cpuinfo.h>
> #include <asm/tlbflush.h>
>
> -static __always_inline void cache_loop(struct page *page, const unsigned int reg)
> +static __always_inline void cache_loop(struct page *page, unsigned long *start,
> + unsigned long *end, const unsigned int reg,
> + const unsigned int cache_type)
> {
> - unsigned long paddr = page_to_pfn(page) << PAGE_SHIFT;
> - unsigned long line = paddr & ~(L1_CACHE_BYTES - 1);
> + unsigned long paddr, next;
>
> - while (line < paddr + PAGE_SIZE) {
> - mtspr(reg, line);
> - line += L1_CACHE_BYTES;
> + if (!cpu_cache_is_present(cache_type))
> + return;
> +
> + if (!cb_inv_flush_is_implemented(reg, cache_type))
> + return;

This check may be a bit overkill, but OK.

> + if (page) {
> + paddr = page_to_pfn(page) << PAGE_SHIFT;
> + next = paddr + PAGE_SIZE;
> + paddr &= ~(L1_CACHE_BYTES - 1);
> + } else if (start && end) {
> + paddr = *start;
> + next = *end;

Overloading the one function with page and start/end seems a bit messy.

It may be nicer to have 2 functions:

cache_loop_page(page, reg, cache_type) {
unsigned long paddr = page_to_pfn(page) << PAGE_SHIFT;
unsiogned long end = paddr + PAGE_SIZE;
paddr &= ~(L1_CACHE_BYTES - 1);
cache_loop(paddr, end, reg, cache_type);
}

cache_loop(start, end, reg, cache_type)

> + } else {
> + printk(KERN_ERR "Missing start and/or end address.\n");
> + return;

Then this could be removed.

> + }
> +
> + while (paddr < next) {
> + mtspr(reg, paddr);
> + paddr += L1_CACHE_BYTES;
> }
> }
>
> void local_dcache_page_flush(struct page *page)
> {
> - cache_loop(page, SPR_DCBFR);
> + cache_loop(page, NULL, NULL, SPR_DCBFR, SPR_UPR_DCP);
> }
> EXPORT_SYMBOL(local_dcache_page_flush);
>
> void local_icache_page_inv(struct page *page)
> {
> - cache_loop(page, SPR_ICBIR);
> + cache_loop(page, NULL, NULL, SPR_ICBIR, SPR_UPR_ICP);
> }
> EXPORT_SYMBOL(local_icache_page_inv);
>
> +void local_dcache_range_flush(unsigned long start, unsigned long end)
> +{
> + cache_loop(NULL, &start, &end, SPR_DCBFR, SPR_UPR_DCP);
> +}
> +
> +void local_dcache_range_inv(unsigned long start, unsigned long end)
> +{
> + cache_loop(NULL, &start, &end, SPR_DCBIR, SPR_UPR_DCP);
> +}
> +
> +void local_icache_range_inv(unsigned long start, unsigned long end)
> +{
> + cache_loop(NULL, &start, &end, SPR_ICBIR, SPR_UPR_ICP);
> +}
> +
> +
> void update_cache(struct vm_area_struct *vma, unsigned long address,
> pte_t *pte)
> {
> diff --git a/arch/openrisc/mm/init.c b/arch/openrisc/mm/init.c
> index d0cb1a0126f9..46b8720db08e 100644
> --- a/arch/openrisc/mm/init.c
> +++ b/arch/openrisc/mm/init.c
> @@ -35,6 +35,7 @@
> #include <asm/fixmap.h>
> #include <asm/tlbflush.h>
> #include <asm/sections.h>
> +#include <asm/cacheflush.h>
>
> int mem_init_done;
>
> @@ -176,8 +177,8 @@ void __init paging_init(void)
> barrier();
>
> /* Invalidate instruction caches after code modification */
> - mtspr(SPR_ICBIR, 0x900);
> - mtspr(SPR_ICBIR, 0xa00);
> + local_icache_block_inv(0x900);
> + local_icache_block_inv(0xa00);

OK.

> /* New TLB miss handlers and kernel page tables are in now place.
> * Make sure that page flags get updated for all pages in TLB by
> --
> 2.48.1
>

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