/* SPDX-License-Identifier: GPL-2.0 */
#ifndef SCATTERLIST_H
#define SCATTERLIST_H
#include <linux/kernel.h>
#include <linux/bug.h>

struct scatterlist {
        unsigned long   page_link;
        unsigned int    offset;
        unsigned int    length;
        dma_addr_t      dma_address;
};

/* Scatterlist helpers, stolen from linux/scatterlist.h */
#define sg_is_chain(sg)         ((sg)->page_link & 0x01)
#define sg_is_last(sg)          ((sg)->page_link & 0x02)
#define sg_chain_ptr(sg)        \
        ((struct scatterlist *) ((sg)->page_link & ~0x03))

/**
 * sg_assign_page - Assign a given page to an SG entry
 * @sg:             SG entry
 * @page:           The page
 *
 * Description:
 *   Assign page to sg entry. Also see sg_set_page(), the most commonly used
 *   variant.
 *
 **/
static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
{
        unsigned long page_link = sg->page_link & 0x3;

        /*
         * In order for the low bit stealing approach to work, pages
         * must be aligned at a 32-bit boundary as a minimum.
         */
        BUG_ON((unsigned long) page & 0x03);
#ifdef CONFIG_DEBUG_SG
        BUG_ON(sg_is_chain(sg));
#endif
        sg->page_link = page_link | (unsigned long) page;
}

/**
 * sg_set_page - Set sg entry to point at given page
 * @sg:          SG entry
 * @page:        The page
 * @len:         Length of data
 * @offset:      Offset into page
 *
 * Description:
 *   Use this function to set an sg entry pointing at a page, never assign
 *   the page directly. We encode sg table information in the lower bits
 *   of the page pointer. See sg_page() for looking up the page belonging
 *   to an sg entry.
 *
 **/
static inline void sg_set_page(struct scatterlist *sg, struct page *page,
                               unsigned int len, unsigned int offset)
{
        sg_assign_page(sg, page);
        sg->offset = offset;
        sg->length = len;
}

static inline struct page *sg_page(struct scatterlist *sg)
{
#ifdef CONFIG_DEBUG_SG
        BUG_ON(sg_is_chain(sg));
#endif
        return (struct page *)((sg)->page_link & ~0x3);
}

/*
 * Loop over each sg element, following the pointer to a new list if necessary
 */
#define for_each_sg(sglist, sg, nr, __i)        \
        for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))

/**
 * sg_chain - Chain two sglists together
 * @prv:        First scatterlist
 * @prv_nents:  Number of entries in prv
 * @sgl:        Second scatterlist
 *
 * Description:
 *   Links @prv@ and @sgl@ together, to form a longer scatterlist.
 *
 **/
static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
                            struct scatterlist *sgl)
{
        /*
         * offset and length are unused for chain entry.  Clear them.
         */
        prv[prv_nents - 1].offset = 0;
        prv[prv_nents - 1].length = 0;

        /*
         * Set lowest bit to indicate a link pointer, and make sure to clear
         * the termination bit if it happens to be set.
         */
        prv[prv_nents - 1].page_link = ((unsigned long) sgl | 0x01) & ~0x02;
}

/**
 * sg_mark_end - Mark the end of the scatterlist
 * @sg:          SG entryScatterlist
 *
 * Description:
 *   Marks the passed in sg entry as the termination point for the sg
 *   table. A call to sg_next() on this entry will return NULL.
 *
 **/
static inline void sg_mark_end(struct scatterlist *sg)
{
        /*
         * Set termination bit, clear potential chain bit
         */
        sg->page_link |= 0x02;
        sg->page_link &= ~0x01;
}

/**
 * sg_unmark_end - Undo setting the end of the scatterlist
 * @sg:          SG entryScatterlist
 *
 * Description:
 *   Removes the termination marker from the given entry of the scatterlist.
 *
 **/
static inline void sg_unmark_end(struct scatterlist *sg)
{
        sg->page_link &= ~0x02;
}

static inline struct scatterlist *sg_next(struct scatterlist *sg)
{
        if (sg_is_last(sg))
                return NULL;

        sg++;
        if (unlikely(sg_is_chain(sg)))
                sg = sg_chain_ptr(sg);

        return sg;
}

static inline void sg_init_table(struct scatterlist *sgl, unsigned int nents)
{
        memset(sgl, 0, sizeof(*sgl) * nents);
        sg_mark_end(&sgl[nents - 1]);
}

static inline dma_addr_t sg_phys(struct scatterlist *sg)
{
        return page_to_phys(sg_page(sg)) + sg->offset;
}

static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
                              unsigned int buflen)
{
        sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
}

static inline void sg_init_one(struct scatterlist *sg,
                               const void *buf, unsigned int buflen)
{
        sg_init_table(sg, 1);
        sg_set_buf(sg, buf, buflen);
}
#endif /* SCATTERLIST_H */