Re: [PATCH PREVIEW RFC 5/6] base: bootcache: Add bootcache memory backend

[Dan Scally <dan.scally@ideasonboard.com>]

Hi Marc

On 26/09/2025 18:34, Marc Kelly wrote:
> Hi Dan,
> 
> There is a yocto build that targets qemuarm64 available at
> https://github.com/The-Good-Penguin/TGP-kernel-cache-test which has
> the latest patches and a script for generating the test cache data as
> a binary for the bootloader to insert into reserved memory.
> 
> There are build instructions and it should be able to run with qemu
> via the commands shown in the readme in the repo.
> 
> If you have any questions don't hesitate to get in touch. Our plan is
> to keep the test distro up to date as we add more features etc as it's
> a covenant way to test and demo things.

Thanks! That's great. I did actually give it a try on a board already and it seems to work well. I 
knocked up a script that's pretty similar to your generate_test_cache.py but parses a yaml file to 
create the .bin and load it and yeah - looks good to me.

I don't know if you're wanting reviews on the patches already yet, but if you let me know when you 
do and CC me on the sets I'll make sure I review them

Thanks
Dan

> 
> Best regards
> Marc.
> 
> On Wed, 24 Sept 2025 at 15:42, Dan Scally <dan.scally@ideasonboard.com> wrote:
>>
>> Hi Andrea
>>
>> On 23/09/2025 15:23, acampanella-thegoodpenguin wrote:
>>> From: Marc Kelly <mkelly@thegoodpenguin.co.uk>
>>>
>>> bootcache_backend_memory provides a simple memory based backend that can
>>> inject data found stored in a reserved-memory block into the bootcache
>>> framework.
>>
>> This looks really cool and I'd like to give it a go; how are you testing it currently? Do you have a
>> tool to create the blob that you're putting into the reserved memory that I could take a look at?
>>
>> Thanks
>> Dan
>>
>>>
>>> Signed-off-by: Marc Kelly <mkelly@thegoodpenguin.co.uk>
>>> ---
>>>    drivers/base/Kconfig                    |   7 +
>>>    drivers/base/Makefile                   |   1 +
>>>    drivers/base/bootcache_backend_memory.c | 220 ++++++++++++++++++++++++++++++++
>>>    3 files changed, 228 insertions(+)
>>>
>>> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
>>> index 1303364993ff4bf7fbbc210243dc6dc48fb1bd83..00c0ea6fa31f2d9a8863c93218a4db7ff87f9c0a 100644
>>> --- a/drivers/base/Kconfig
>>> +++ b/drivers/base/Kconfig
>>> @@ -95,6 +95,13 @@ config BOOTCACHE
>>>                  A simple backend for testing and development.
>>>                  It does not persist any data externally.
>>>
>>> +     config BOOTCACHE_BACKEND_MEMORY
>>> +             bool "Memory backend"
>>> +             help
>>> +               A backend that reads the cache data from reserved system memory.
>>> +               The reserved memory block is defined in the device tree and is
>>> +               assumed to be populated by the bootloader.
>>> +
>>>        endchoice
>>>        endif
>>>
>>> diff --git a/drivers/base/Makefile b/drivers/base/Makefile
>>> index dc87c21cd79468045878c4b3cef5714c12f65ec4..d818e72df290e6772297345efc71082adc04e1f2 100644
>>> --- a/drivers/base/Makefile
>>> +++ b/drivers/base/Makefile
>>> @@ -10,6 +10,7 @@ obj-y                       := component.o core.o bus.o dd.o syscore.o \
>>>    obj-$(CONFIG_AUXILIARY_BUS) += auxiliary.o
>>>    obj-$(CONFIG_BOOTCACHE)    += bootcache.o
>>>    obj-$(CONFIG_BOOTCACHE_BACKEND_TEST)    += bootcache_backend_test.o
>>> +obj-$(CONFIG_BOOTCACHE_BACKEND_MEMORY)    += bootcache_backend_memory.o
>>>    obj-$(CONFIG_DEVTMPFS)      += devtmpfs.o
>>>    obj-y                       += power/
>>>    obj-$(CONFIG_ISA_BUS_API)   += isa.o
>>> diff --git a/drivers/base/bootcache_backend_memory.c b/drivers/base/bootcache_backend_memory.c
>>> new file mode 100644
>>> index 0000000000000000000000000000000000000000..d7a83ce2725bc7aa5f37d5fc3dcd7bea753e4d68
>>> --- /dev/null
>>> +++ b/drivers/base/bootcache_backend_memory.c
>>> @@ -0,0 +1,220 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +#define DEBUG 1
>>> +#include <linux/unaligned.h>
>>> +#include <linux/init.h>
>>> +#include <linux/io.h>
>>> +#include <linux/kernel.h>
>>> +#include <linux/slab.h>
>>> +#include <linux/hashtable.h>
>>> +#include <linux/of.h>
>>> +#include <linux/of_device.h>
>>> +#include <linux/of_reserved_mem.h>
>>> +#include <linux/platform_device.h>
>>> +#include <linux/string.h>
>>> +#include <linux/types.h>
>>> +#include <linux/errno.h>
>>> +#include <linux/kobject.h>
>>> +#include <linux/sysfs.h>
>>> +
>>> +#include <linux/bootcache.h>
>>> +
>>> +#define DRIVER_NAME "bootcache_memory_backend"
>>> +#define BOOTCACHE_MAGIC ('B' << 24 | 'C' << 16 | 'H' << 8 | 'E')
>>> +#define BOOTCACHE_MINSIZE 4096
>>> +
>>> +/*
>>> + * This defines a cache entry as stored.
>>> + */
>>> +struct cache_memory_store_entry {
>>> +     u32 key_length;
>>> +     u32 data_length;
>>> +     u8 data_type;
>>> +     u8 data[];
>>> +} __packed;
>>> +
>>> +/*
>>> + * The in memory store of multiple cache entries.
>>> + */
>>> +struct cache_memory_store {
>>> +     u32 magic;
>>> +     u32 entry_count;
>>> +     struct cache_memory_store_entry entries[];
>>> +} __packed;
>>> +
>>> +struct reserved_mem *rmem;
>>> +
>>> +/*
>>> + * This function processes the loaded data and adds each entry to the
>>> + * system cache via the callbck.
>>> + */
>>> +static int memory_backend_load_cache(void)
>>> +{
>>> +     const struct cache_memory_store *store;
>>> +     const u8 *current_ptr;
>>> +     const void *max_address;
>>> +     u32 entry_count;
>>> +     int i;
>>> +     int ret;
>>> +
>>> +     if (!rmem) {
>>> +             pr_warn("%s: No bootcache was found\n", DRIVER_NAME);
>>> +             return 0;
>>> +     }
>>> +
>>> +     store = ioremap(rmem->base, rmem->size);
>>> +     if (!store) {
>>> +             pr_warn("%s: Unable to map reserved memory 0x%llx\n", DRIVER_NAME, rmem->base);
>>> +             return -ENOMEM;
>>> +     }
>>> +     max_address = store + rmem->size;
>>> +     current_ptr = (const unsigned char *)store->entries;
>>> +     entry_count = get_unaligned(&store->entry_count);
>>> +
>>> +     for (i = 0; i < entry_count; i++) {
>>> +             struct cache_memory_store_entry *entry;
>>> +             struct bootcache_entry *new_entry = NULL;
>>> +             size_t data_length, key_length;
>>> +             u8 *src, *dest;
>>> +             int j;
>>> +
>>> +             entry = (struct cache_memory_store_entry *)current_ptr;
>>> +             data_length = get_unaligned(&entry->data_length);
>>> +             key_length = get_unaligned(&entry->key_length);
>>> +
>>> +             /* Check if will go outside the bounds */
>>> +             if ((current_ptr + sizeof(struct cache_memory_store_entry) +
>>> +                             data_length + key_length + 1) > max_address) {
>>> +                     ret = -ENOMEM;
>>> +                     goto error;
>>> +             }
>>> +
>>> +             new_entry = kzalloc(sizeof(*new_entry), GFP_KERNEL);
>>> +             if (!new_entry) {
>>> +                     ret = -ENOMEM;
>>> +                     goto error;
>>> +             }
>>> +
>>> +             new_entry->len = data_length;
>>> +             new_entry->key = kzalloc(key_length+1, GFP_KERNEL);
>>> +             new_entry->data = kzalloc(data_length, GFP_KERNEL);
>>> +
>>> +             if (!new_entry->key || !new_entry->data) {
>>> +                     pr_err("%s: Memory Allocation error creating new_entry data\n",
>>> +                             DRIVER_NAME);
>>> +                     kfree(new_entry->key);
>>> +                     kfree(new_entry->data);
>>> +                     kfree(new_entry);
>>> +                     ret = -ENOMEM;
>>> +                     goto error;
>>> +             }
>>> +             /*
>>> +              * Source data is potentially unaligned, so we copy it with the correct
>>> +              * access functions
>>> +              */
>>> +             src = &entry->data[0];
>>> +             dest = new_entry->key;
>>> +             for (j = 0; j < key_length; j++)
>>> +                     *dest++ = get_unaligned(src++);
>>> +
>>> +             src = &entry->data[key_length+1];
>>> +             dest = new_entry->data;
>>> +             for (j = 0; j < data_length; j++)
>>> +                     *dest++ = get_unaligned(src++);
>>> +
>>> +             pr_debug("%s: Setting up Entry (%d) with key: %s, data length is %zu\n",
>>> +                     DRIVER_NAME, i, new_entry->key, new_entry->len);
>>> +
>>> +             /* call the framework provided function */
>>> +             ret = bootcache_add_entry(new_entry);
>>> +             if (ret) {
>>> +                     kfree(new_entry->key);
>>> +                     kfree(new_entry->data);
>>> +                     kfree(new_entry);
>>> +                     ret = 0;
>>> +             }
>>> +
>>> +             /* Sanity check we've got space for the next extry */
>>> +
>>> +             current_ptr += sizeof(struct cache_memory_store_entry) +
>>> +                     data_length + key_length + 1;
>>> +             if (current_ptr + sizeof(struct cache_memory_store_entry)
>>> +                             > max_address) {
>>> +                     ret = ret = -ENOMEM;
>>> +                     goto error;
>>> +             }
>>> +     }
>>> +
>>> +error:
>>> +     if (store)
>>> +             iounmap((void *)store);
>>> +
>>> +     return ret;
>>> +}
>>> +
>>> +static struct bootcache_info cache_info = {
>>> +     .name = "memory",
>>> +     .load_cache = memory_backend_load_cache,
>>> +};
>>> +
>>> +static int bootcache_backend_probe(struct platform_device *pdev)
>>> +{
>>> +     int ret;
>>> +     size_t table_size;
>>> +     struct cache_memory_store *temp_store;
>>> +     struct device_node *reserved_mem_node;
>>> +
>>> +     /* Check for the front end being ready */
>>> +
>>> +     pr_debug("%s: %s\n", DRIVER_NAME, __func__);
>>> +
>>> +     reserved_mem_node = of_parse_phandle(pdev->dev.of_node, "memory-region", 0);
>>> +     if (reserved_mem_node) {
>>> +             rmem = of_reserved_mem_lookup(reserved_mem_node);
>>> +             of_node_put(reserved_mem_node);
>>> +     }
>>> +
>>> +     if (!rmem) {
>>> +             pr_err("%s: Failed to find reserved memory region.\n", DRIVER_NAME);
>>> +             return -ENOMEM;
>>> +     }
>>> +     pr_debug("%s: Found reserved cache memory block (%s):\n", DRIVER_NAME, rmem->name);
>>> +     pr_debug("%s:  Physical Address: 0x%llx\n", DRIVER_NAME, rmem->base);
>>> +     pr_debug("%s:  Size: 0x%llx (%llu bytes)\n", DRIVER_NAME, rmem->size,
>>> +             rmem->size);
>>> +
>>> +     if (rmem->size < BOOTCACHE_MINSIZE) {
>>> +             pr_err("%s: reserved memory too small (%llu bytes)\n", DRIVER_NAME, rmem->size);
>>> +             return -ENOMEM;
>>> +     }
>>> +
>>> +     ret = bootcache_register_backend(&cache_info);
>>> +
>>> +     if (ret < 0) {
>>> +             pr_err("%s: bootcache_register_backend() failed with error %d\n",
>>> +                     DRIVER_NAME, ret);
>>> +             return ret;
>>> +     }
>>> +     pr_info("%s: Backend loaded\n", DRIVER_NAME);
>>> +
>>> +     return 0;
>>> +}
>>> +
>>> +static const struct of_device_id bootcache_backend_driver_dt_ids[] = {
>>> +     { .compatible = "linux,backend-backend-memory", },
>>> +     { }
>>> +};
>>> +
>>> +static struct platform_driver bootcache_memory_platform_driver = {
>>> +     .probe          = bootcache_backend_probe,
>>> +     .driver         = {
>>> +             .name   = DRIVER_NAME,
>>> +             .of_match_table = of_match_ptr(bootcache_backend_driver_dt_ids),
>>> +     },
>>> +};
>>> +
>>> +static int __init bootcache_backend_init(void)
>>> +{
>>> +     return platform_driver_register(&bootcache_memory_platform_driver);
>>> +}
>>> +
>>> +core_initcall(bootcache_backend_init);
>>>
>>
>>
> 
>