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    SubjectRe: [PATCH v2,RESEND] misc: new driver sram uapi for user level SRAM access
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    Hi, Scott, Greg,

    Thank you for your helpful comments.
    For that Greg mentioned that the patch (or patch series) via UIO should worked through,
    so I want to make it clear that if it would go upstream?(And if so, when? No push, just ask)

    Also I have been wondering how the patches with components in different subsystems
    go get upstream to the mainline? Like patch 1-3 are of linuxppc-dev, and patch 4 is of
    subsystem UIO, and if acceptable, how would you deal with them?

    Back to the devicetree thing, I make it detached from hardware compatibilities which belong
    to the hardware level driver and also used module parameter for of_id definition as dt-binding
    is not allowed for UIO now. So as I can see, things may go well and there is no harm to anything,
    I hope you(Scott) please take a re-consideration.

    Thanks & regards,
    Wenhu

    >On Sun, 2020-04-19 at 20:05 -0700, Wang Wenhu wrote:
    >> +static void sram_uapi_res_insert(struct sram_uapi *uapi,
    >> + struct sram_resource *res)
    >> +{
    >> + struct sram_resource *cur, *tmp;
    >> + struct list_head *head = &uapi->res_list;
    >> +
    >> + list_for_each_entry_safe(cur, tmp, head, list) {
    >> + if (&tmp->list != head &&
    >> + (cur->info.offset + cur->info.size + res->info.size <=
    >> + tmp->info.offset)) {
    >> + res->info.offset = cur->info.offset + cur->info.size;
    >> + res->parent = uapi;
    >> + list_add(&res->list, &cur->list);
    >> + return;
    >> + }
    >> + }
    >
    >We don't need yet another open coded allocator. If you really need to do this
    >then use include/linux/genalloc.h, but maybe keep it simple and just have one
    >allocaton per file descriptor so you don't need to manage fd offsets?
    >
    >> +static struct sram_resource *sram_uapi_find_res(struct sram_uapi *uapi,
    >> + __u32 offset)
    >> +{
    >> + struct sram_resource *res;
    >> +
    >> + list_for_each_entry(res, &uapi->res_list, list) {
    >> + if (res->info.offset == offset)
    >> + return res;
    >> + }
    >> +
    >> + return NULL;
    >> +}
    >
    >What if the allocation is more than one page, and the user mmaps starting
    >somewhere other than the first page?
    >
    >> + switch (cmd) {
    >> + case SRAM_UAPI_IOC_SET_SRAM_TYPE:
    >> + if (uapi->sa)
    >> + return -EEXIST;
    >> +
    >> + get_user(type, (const __u32 __user *)arg);
    >> + uapi->sa = get_sram_api_from_type(type);
    >> + if (uapi->sa)
    >> + ret = 0;
    >> + else
    >> + ret = -ENODEV;
    >> +
    >> + break;
    >> +
    >
    >Just expose one device per backing SRAM, especially if the user has any reason
    >to care about where the SRAM is coming from (correlating sysfs nodes is much
    >more expressive than some vague notion of "type").
    >
    >> + case SRAM_UAPI_IOC_ALLOC:
    >> + if (!uapi->sa)
    >> + return -EINVAL;
    >> +
    >> + res = kzalloc(sizeof(*res), GFP_KERNEL);
    >> + if (!res)
    >> + return -ENOMEM;
    >> +
    >> + size = copy_from_user((void *)&res->info,
    >> + (const void __user *)arg,
    >> + sizeof(res->info));
    >> + if (!PAGE_ALIGNED(res->info.size) || !res->info.size)
    >> + return -EINVAL;
    >
    >Missing EFAULT test (here and elsewhere), and res leaks on error.
    >
    >> +
    >> + res->virt = (void *)uapi->sa->sram_alloc(res->info.size,
    >> + &res->phys,
    >> + PAGE_SIZE);
    >
    >Do we really need multiple allocators, or could the backend be limited to just
    >adding regions to a generic allocator (with that allocator also serving in-
    >kernel users)?
    >
    >If sram_alloc is supposed to return a virtual address, why isn't that the
    >return type?
    >
    >> + if (!res->virt) {
    >> + kfree(res);
    >> + return -ENOMEM;
    >> + }
    >
    >ENOSPC might be more appropriate, as this isn't general-purpose RAM.
    >
    >> +
    >> + sram_uapi_res_insert(uapi, res);
    >> + size = copy_to_user((void __user *)arg,
    >> + (const void *)&res->info,
    >> + sizeof(res->info));
    >> +
    >> + ret = 0;
    >> + break;
    >> +
    >> + case SRAM_UAPI_IOC_FREE:
    >> + if (!uapi->sa)
    >> + return -EINVAL;
    >> +
    >> + size = copy_from_user((void *)&info, (const void __user *)arg,
    >> + sizeof(info));
    >> +
    >> + res = sram_uapi_res_delete(uapi, &info);
    >> + if (!res) {
    >> + pr_err("error no sram resource found\n");
    >> + return -EINVAL;
    >> + }
    >> +
    >> + uapi->sa->sram_free(res->virt);
    >> + kfree(res);
    >> +
    >> + ret = 0;
    >> + break;
    >
    >So you can just delete any arbitrary offset, even if you weren't the one that
    >allocated it? Even if this isn't meant for unprivileged use it seems error-
    >prone.
    >
    >> +
    >> + default:
    >> + pr_err("error no cmd not supported\n");
    >> + break;
    >> + }
    >> +
    >> + return ret;
    >> +}
    >> +
    >> +static int sram_uapi_mmap(struct file *filp, struct vm_area_struct *vma)
    >> +{
    >> + struct sram_uapi *uapi = filp->private_data;
    >> + struct sram_resource *res;
    >> +
    >> + res = sram_uapi_find_res(uapi, vma->vm_pgoff);
    >> + if (!res)
    >> + return -EINVAL;
    >> +
    >> + if (vma->vm_end - vma->vm_start > res->info.size)
    >> + return -EINVAL;
    >> +
    >> + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
    >> +
    >> + return remap_pfn_range(vma, vma->vm_start,
    >> + res->phys >> PAGE_SHIFT,
    >> + vma->vm_end - vma->vm_start,
    >> + vma->vm_page_prot);
    >> +}
    >
    >Will noncached always be what's wanted here?
    >
    >-Scott
    >
    >


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