From: Nathan Lynch <nathan.lynch@xxxxxxx> Import the example code from the "SDXI Descriptor Ring Operation" chapter of the SDXI 1.0 spec[1], which demonstrates lockless descriptor submission to the ring. Lightly alter the code to (somewhat) comply with Linux coding style, and use byte order-aware types as well as kernel atomic and barrier APIs. Ultimately we may not really need a lockless submission path, and it would be better for it to more closely integrate with the rest of the driver. [1] https://www.snia.org/sites/default/files/technical-work/sdxi/release/SNIA-SDXI-Specification-v1.0a.pdf Signed-off-by: Nathan Lynch <nathan.lynch@xxxxxxx> --- drivers/dma/sdxi/enqueue.c | 136 +++++++++++++++++++++++++++++++++++++++++++++ drivers/dma/sdxi/enqueue.h | 16 ++++++ 2 files changed, 152 insertions(+) diff --git a/drivers/dma/sdxi/enqueue.c b/drivers/dma/sdxi/enqueue.c new file mode 100644 index 0000000000000000000000000000000000000000..822d9b890fa3538dcc09e99ef562a6d8419290f0 --- /dev/null +++ b/drivers/dma/sdxi/enqueue.c @@ -0,0 +1,136 @@ +// SPDX-License-Identifier: BSD-3-Clause +/* + * + * Copyright (c) 2024, The Storage Networking Industry Association. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * + * * Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * + * * Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the + * distribution. + * + * * Neither the name of The Storage Networking Industry Association + * (SNIA) nor the names of its contributors may be used to endorse or + * promote products derived from this software without specific prior + * written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS + * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE + * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES + * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR + * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, + * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED + * OF THE POSSIBILITY OF SUCH DAMAGE. + */ + +#include <asm/barrier.h> +#include <asm/byteorder.h> +#include <asm/rwonce.h> +#include <linux/atomic.h> +#include <linux/errno.h> +#include <linux/io-64-nonatomic-lo-hi.h> +#include <linux/processor.h> +#include <linux/types.h> + +#include "enqueue.h" + +/* + * Code adapted from the "SDXI Descriptor Ring Operation" chapter of + * the SDXI spec, specifically the example code in "Enqueuing one or + * more Descriptors." + */ + +#define SDXI_DESCR_SIZE 64 +#define SDXI_DS_NUM_QW (SDXI_DESCR_SIZE / sizeof(__le64)) +#define SDXI_MULTI_PRODUCER 1 /* Define to 0 if single-producer. */ + +static int update_ring(const __le64 *enq_entries, /* Ptr to entries to enqueue */ + u64 enq_num, /* Number of entries to enqueue */ + __le64 *ring_base, /* Ptr to ring location */ + u64 ring_size, /* (Ring Size in bytes)/64 */ + u64 index) /* Starting ring index to update */ +{ + for (u64 i = 0; i < enq_num; i++) { + __le64 *ringp = ring_base + ((index + i) % ring_size) * SDXI_DS_NUM_QW; + const __le64 *entryp = enq_entries + (i * SDXI_DS_NUM_QW); + + for (u64 j = 1; j < SDXI_DS_NUM_QW; j++) + *(ringp + j) = *(entryp + j); + } + + /* Now write the first QW of the new entries to the ring. */ + dma_wmb(); + for (u64 i = 0; i < enq_num; i++) { + __le64 *ringp = ring_base + ((index + i) % ring_size) * SDXI_DS_NUM_QW; + const __le64 *entryp = enq_entries + (i * SDXI_DS_NUM_QW); + + *ringp = *entryp; + } + + return 0; +} + +int sdxi_enqueue(const __le64 *enq_entries, /* Ptr to entries to enqueue */ + u64 enq_num, /* Number of entries to enqueue */ + __le64 *ring_base, /* Ptr to ring location */ + u64 ring_size, /* (Ring Size in bytes)/64 */ + __le64 const volatile * const Read_Index, /* Ptr to Read_Index location */ + __le64 volatile * const Write_Index, /* Ptr to Write_Index location */ + __le64 __iomem *Door_Bell) /* Ptr to Ring Doorbell location */ +{ + u64 old_write_idx; + u64 new_idx; + + while (true) { + u64 read_idx; + + read_idx = le64_to_cpu(READ_ONCE(*Read_Index)); + dma_rmb(); /* Get Read_Index before Write_Index to always get consistent values */ + old_write_idx = le64_to_cpu(READ_ONCE(*Write_Index)); + + if (read_idx > old_write_idx) { + /* Only happens if Write_Index wraps or ring has bad setup */ + return -EIO; + } + + new_idx = old_write_idx + enq_num; + if (new_idx - read_idx > ring_size) { + cpu_relax(); + continue; /* Not enough free entries, try again */ + } + + if (SDXI_MULTI_PRODUCER) { + /* Try to atomically update Write_Index. */ + bool success = cmpxchg(Write_Index, + cpu_to_le64(old_write_idx), + cpu_to_le64(new_idx)) == cpu_to_le64(old_write_idx); + if (success) + break; /* Updated Write_Index, no need to try again. */ + } else { + /* Single-Producer case */ + WRITE_ONCE(*Write_Index, cpu_to_le64(new_idx)); + dma_wmb(); /* Make the Write_Index update visible before the Door_Bell update. */ + break; /* Always successful for single-producer */ + } + /* Couldn"t update Write_Index, try again. */ + } + + /* Write_Index is now advanced. Let's write out entries to the ring. */ + update_ring(enq_entries, enq_num, ring_base, ring_size, old_write_idx); + + /* Door_Bell write required; only needs ordering wrt update of Write_Index. */ + iowrite64(new_idx, Door_Bell); + + return 0; +} diff --git a/drivers/dma/sdxi/enqueue.h b/drivers/dma/sdxi/enqueue.h new file mode 100644 index 0000000000000000000000000000000000000000..28c1493779db1119ff0d682fa6623b016998042a --- /dev/null +++ b/drivers/dma/sdxi/enqueue.h @@ -0,0 +1,16 @@ +/* SPDX-License-Identifier: BSD-3-Clause */ +/* Copyright (c) 2024, The Storage Networking Industry Association. */ +#ifndef DMA_SDXI_ENQUEUE_H +#define DMA_SDXI_ENQUEUE_H + +#include <linux/types.h> + +int sdxi_enqueue(const __le64 *enq_entries, /* Ptr to entries to enqueue */ + u64 enq_num, /* Number of entries to enqueue */ + __le64 *ring_base, /* Ptr to ring location */ + u64 ring_size, /* (Ring Size in bytes)/64 */ + __le64 const volatile * const Read_Index, /* Ptr to Read_Index location */ + __le64 volatile * const Write_Index, /* Ptr to Write_Index location */ + __le64 __iomem *Door_Bell); /* Ptr to Ring Doorbell location */ + +#endif /* DMA_SDXI_ENQUEUE_H */ -- 2.39.5
