Re: [PATCH v2] openrisc: Add cacheinfo support

Sahil Siddiq
2025-03-17T18:36:37Z

Hello Stafford and Geert,

Thank you for the reviews.

On 3/17/25 1:55 PM, Geert Uytterhoeven wrote:
> On Sun, 16 Mar 2025 at 07:59, Stafford Horne <shorne@gmail.com> wrote:
>> [...]
>>> +struct cache_desc {
>>> + u32 size;
>>> + u32 sets;
>>> + u32 block_size;
>>> + u32 ways;
>>
>> Considering the changes below to add cache available checks, maybe we
>> want to add a field here, such as `bool present`. Or a flags field like
>> is used in loongarch?
>
> I assume cache_desc.size is zero when the cache is not present?

Yes, cache_desc.size will be zero when there's no cache component since
cpuinfo_or1k[NR_CPUS] is declared as a global variable in setup.c. The
cache attributes are stored in this struct.

On 3/17/25 5:30 PM, Stafford Horne wrote:
> [...]
> Yes, good point, would be clean too work too. I was not too happy with using
> cache_desc.ways as is done below. Also there ended up bieng 2 different ways
> that were used.
>
> I am happy to use size too, but I think checking the SPR would be faster or just
> as fast as using the struct. I am not too fussed either way.

There are a few places (e.g. cache_loop() in cache.c) where
cpuinfo_or1k[smp_processor_id()] is not being referenced. This will have to be
referenced to access cache_desc. In these cases, I think it would be better to
read from the SPR instead. For consistency, the SPR can also be read where
cpuinfo_or1k[smp_processor_id()] is already being referenced.

On 3/16/25 12:28 PM, Stafford Horne wrote:
> On Sun, Mar 16, 2025 at 02:09:37AM +0530, Sahil Siddiq wrote:
>> Add cacheinfo support for OpenRISC.
>> [...]
>> diff --git a/arch/openrisc/kernel/cacheinfo.c b/arch/openrisc/kernel/cacheinfo.c
>> new file mode 100644
>> index 000000000000..6bb81e246f7e
>> --- /dev/null
>> +++ b/arch/openrisc/kernel/cacheinfo.c
>> @@ -0,0 +1,106 @@
>> +// SPDX-License-Identifier: GPL-2.0-or-later
>> +/*
>> + * OpenRISC cacheinfo support
>> + *
>> + * Based on work done for MIPS and LoongArch. All original copyrights
>> + * apply as per the original source declaration.
>> + *
>> + * OpenRISC implementation:
>> + * Copyright (C) 2025 Sahil Siddiq <sahilcdq@proton.me>
>> + */
>> +
>> +#include <linux/cacheinfo.h>
>> +#include <asm/cpuinfo.h>
>> +#include <asm/spr.h>
>> +#include <asm/spr_defs.h>
>> +
>> +static inline void ci_leaf_init(struct cacheinfo *this_leaf, enum cache_type type,
>> + unsigned int level, struct cache_desc *cache, int cpu)
>> +{
>> + this_leaf->type = type;
>> + this_leaf->level = level;
>> + this_leaf->coherency_line_size = cache->block_size;
>> + this_leaf->number_of_sets = cache->sets;
>> + this_leaf->ways_of_associativity = cache->ways;
>> + this_leaf->size = cache->size;
>> + cpumask_set_cpu(cpu, &this_leaf->shared_cpu_map);
>> +}
>> +
>> +int init_cache_level(unsigned int cpu)
>> +{
>> + struct cpuinfo_or1k *cpuinfo = &cpuinfo_or1k[smp_processor_id()];
>> + struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
>> + int leaves = 0, levels = 0;
>> + unsigned long upr = mfspr(SPR_UPR);
>> + unsigned long iccfgr, dccfgr;
>> +
>> + if (!(upr & SPR_UPR_UP)) {
>> + printk(KERN_INFO
>> + "-- no UPR register... unable to detect configuration\n");
>> + return -ENOENT;
>> + }
>> +
>> + if (upr & SPR_UPR_DCP) {
>> + dccfgr = mfspr(SPR_DCCFGR);
>> + cpuinfo->dcache.ways = 1 << (dccfgr & SPR_DCCFGR_NCW);
>> + cpuinfo->dcache.sets = 1 << ((dccfgr & SPR_DCCFGR_NCS) >> 3);
>> + cpuinfo->dcache.block_size = 16 << ((dccfgr & SPR_DCCFGR_CBS) >> 7);
>> + cpuinfo->dcache.size =
>> + cpuinfo->dcache.sets * cpuinfo->dcache.ways * cpuinfo->dcache.block_size;
>> + leaves += 1;
>> + printk(KERN_INFO
>> + "-- dcache: %d bytes total, %d bytes/line, %d set(s), %d way(s)\n",
>> + cpuinfo->dcache.size, cpuinfo->dcache.block_size,
>> + cpuinfo->dcache.sets,
>> + cpuinfo->dcache.ways);
>
> The indentation of sets looks a bit off here.
>
>> + } else
>> + printk(KERN_INFO "-- dcache disabled\n");
>> +
>> + if (upr & SPR_UPR_ICP) {
>> + iccfgr = mfspr(SPR_ICCFGR);
>> + cpuinfo->icache.ways = 1 << (iccfgr & SPR_ICCFGR_NCW);
>> + cpuinfo->icache.sets = 1 << ((iccfgr & SPR_ICCFGR_NCS) >> 3);
>> + cpuinfo->icache.block_size = 16 << ((iccfgr & SPR_ICCFGR_CBS) >> 7);
>> + cpuinfo->icache.size =
>> + cpuinfo->icache.sets * cpuinfo->icache.ways * cpuinfo->icache.block_size;
>> + leaves += 1;
>> + printk(KERN_INFO
>> + "-- icache: %d bytes total, %d bytes/line, %d set(s), %d way(s)\n",
>> + cpuinfo->icache.size, cpuinfo->icache.block_size,
>> + cpuinfo->icache.sets,
>> + cpuinfo->icache.ways);
>
> The indentation of sets looks a bit off here. Maybe its the others that are out
> of line, but can you fix? Also I think sets and ways could be on the same line.

Sorry, I must have missed this. I'll fix it.

>> [...]
>> diff --git a/arch/openrisc/kernel/dma.c b/arch/openrisc/kernel/dma.c
>> index b3edbb33b621..ffb161e41e9d 100644
>> --- a/arch/openrisc/kernel/dma.c
>> +++ b/arch/openrisc/kernel/dma.c
>> @@ -36,8 +36,10 @@ 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);
>> + if (cpuinfo->dcache.ways) {
>> + for (cl = __pa(addr); cl < __pa(next); cl += cpuinfo->dcache.block_size)
>> + mtspr(SPR_DCBFR, cl);
>> + }
>
> I think it would be better to move this to cacheflush.h as a function like
> flush_dcache_range() or local_dcache_range_flush().
>
>> return 0;
>> }
>> @@ -104,15 +106,19 @@ void arch_sync_dma_for_device(phys_addr_t addr, size_t size,
>> 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);
>> + if (cpuinfo->dcache.ways) {
>> + for (cl = addr; cl < addr + size;
>> + cl += cpuinfo->dcache.block_size)
>> + mtspr(SPR_DCBFR, cl);
>> + }
>
> Also here,I think it would be better to move this to cacheflush.h as a function like
> flush_dcache_range().
>
> Or, local_dcache_range_flush(), which seems to be the convention we use in
> cacheflush.h/cache.c.
>
>
>> 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);
>> + if (cpuinfo->dcache.ways) {
>> + for (cl = addr; cl < addr + size;
>> + cl += cpuinfo->dcache.block_size)
>> + mtspr(SPR_DCBIR, cl);
>> + }
>
> This one could be invalidate_dcache_range(). Note, this will also be useful
> for the kexec patches that I am working on.
>
> Or, local_dcache_range_inv(), which seems to be the convention we use in
> cacheflush.h/cache.c.

Understood.

>> [...]
>> @@ -29,13 +34,13 @@ static __always_inline void cache_loop(struct page *page, const unsigned int reg
>>
>> void local_dcache_page_flush(struct page *page)
>> {
>> - cache_loop(page, SPR_DCBFR);
>> + cache_loop(page, 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, SPR_ICBIR, SPR_UPR_ICP);
>> }
>> EXPORT_SYMBOL(local_icache_page_inv);
>
> OK, if we move the range flush and invalidate here we will need to add to this
> cache_loop a bit more.

Right. I'll see what can be done to keep it concise.

>> diff --git a/arch/openrisc/mm/init.c b/arch/openrisc/mm/init.c
>> index d0cb1a0126f9..bbe16546c5b9 100644
>> --- a/arch/openrisc/mm/init.c
>> +++ b/arch/openrisc/mm/init.c
>> @@ -124,6 +124,7 @@ static void __init map_ram(void)
>> void __init paging_init(void)
>> {
>> int i;
>> + unsigned long upr;
>>
>> printk(KERN_INFO "Setting up paging and PTEs.\n");
>>
>> @@ -176,8 +177,11 @@ void __init paging_init(void)
>> barrier();
>>
>> /* Invalidate instruction caches after code modification */
>> - mtspr(SPR_ICBIR, 0x900);
>> - mtspr(SPR_ICBIR, 0xa00);
>> + upr = mfspr(SPR_UPR);
>> + if (upr & SPR_UPR_UP & SPR_UPR_ICP) {
>> + mtspr(SPR_ICBIR, 0x900);
>> + mtspr(SPR_ICBIR, 0xa00);
>> + }
>
> Here we could use new utilities such as local_icache_range_inv(0x900,
> L1_CACHE_BYTES);
>
> Or something like local_icache_block_inv(0x900). This only needs to flush a
> single block as the code it is invalidating is just 2 instructions 8 bytes:
>
> .org 0x900
> l.j boot_dtlb_miss_handler
> l.nop
>
> .org 0xa00
> l.j boot_itlb_miss_handler
> l.nop

Given that there'll be generic local_(i|d)cache_range_inv(start, stop) utility
functions, would it make sense to simply have a macro defined as:

#define local_icache_block_inv(addr) local_icache_range_inv(start, L1_CACHE_BYTES)

instead of having a separate function for invalidating a single cache line? This would
still use cache_loop() under the hood. The alternative would be to use
local_icache_range_inv(start, L1_CACHE_BYTES) directly but using the macro might be
more readable.

Thanks,
Sahil