Re: [RFC v2 PATCH 04/10] net: ti: prueth: Adds link detection, RX and TX support.

Basharath Hussain Khaja
2025-01-29T05:43:06Z

> On Fri, Jan 24, 2025 at 06:07:01PM +0530, Basharath Hussain Khaja wrote:
>> From: Roger Quadros <rogerq@ti.com>
>>
>> Changes corresponding to link configuration such as speed and duplexity.
>> IRQ and handler initializations are performed for packet reception.Firmware
>> receives the packet from the wire and stores it into OCMC queue. Next, it
>> notifies the CPU via interrupt. Upon receiving the interrupt CPU will
>> service the IRQ and packet will be processed by pushing the newly allocated
>> SKB to upper layers.
>>
>> When the user application want to transmit a packet, it will invoke
>> sys_send() which will inturn invoke the PRUETH driver, then it will write
>> the packet into OCMC queues. PRU firmware will pick up the packet and
>> transmit it on to the wire.
>>
>> Signed-off-by: Roger Quadros <rogerq@ti.com>
>> Signed-off-by: Andrew F. Davis <afd@ti.com>
>> Signed-off-by: Parvathi Pudi <parvathi@couthit.com>
>> Signed-off-by: Basharath Hussain Khaja <basharath@couthit.com>
>> ---
>> drivers/net/ethernet/ti/icssm/icssm_prueth.c | 599 ++++++++++++++++++-
>> drivers/net/ethernet/ti/icssm/icssm_prueth.h | 46 ++
>> 2 files changed, 640 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/ti/icssm/icssm_prueth.c
>> b/drivers/net/ethernet/ti/icssm/icssm_prueth.c
>> index 82ed0e3a0d88..0ba1d16a7a15 100644
>> --- a/drivers/net/ethernet/ti/icssm/icssm_prueth.c
>> +++ b/drivers/net/ethernet/ti/icssm/icssm_prueth.c
>
> [...]
>
>> +/**
>> + * icssm_prueth_tx_enqueue - queue a packet to firmware for transmission
>> + *
>> + * @emac: EMAC data structure
>> + * @skb: packet data buffer
>> + * @queue_id: priority queue id
>> + *
>> + * Return: 0 (Success)
>> + */
>> +static int icssm_prueth_tx_enqueue(struct prueth_emac *emac,
>> + struct sk_buff *skb,
>> + enum prueth_queue_id queue_id)
>> +{
>
> [...]
>
>> +
>> + /* which port to tx: MII0 or MII1 */
>> + txport = emac->tx_port_queue;
>> + src_addr = skb->data;
>> + pktlen = skb->len;
>> + /* Get the tx queue */
>> + queue_desc = emac->tx_queue_descs + queue_id;
>> + txqueue = &queue_infos[txport][queue_id];
>> +
>> + buffer_desc_count = txqueue->buffer_desc_end -
>> + txqueue->buffer_desc_offset;
>> + buffer_desc_count /= BD_SIZE;
>> + buffer_desc_count++;
>> +
>> + bd_rd_ptr = readw(&queue_desc->rd_ptr);
>> + bd_wr_ptr = readw(&queue_desc->wr_ptr);
>> +
>> + /* the PRU firmware deals mostly in pointers already
>> + * offset into ram, we would like to deal in indexes
>> + * within the queue we are working with for code
>> + * simplicity, calculate this here
>> + */
>> + write_block = (bd_wr_ptr - txqueue->buffer_desc_offset) / BD_SIZE;
>> + read_block = (bd_rd_ptr - txqueue->buffer_desc_offset) / BD_SIZE;
>
> Seems like there's a lot of similar code repeated in the rx code
> path.
>
> Maybe there's a way to simplify it all with a helper of some sort?
>

We will plan to re-look into common code (more than twice) and create a helper
function and use it.

>> + if (write_block > read_block) {
>> + free_blocks = buffer_desc_count - write_block;
>> + free_blocks += read_block;
>> + } else if (write_block < read_block) {
>> + free_blocks = read_block - write_block;
>> + } else { /* they are all free */
>> + free_blocks = buffer_desc_count;
>> + }
>> +
>> + pkt_block_size = DIV_ROUND_UP(pktlen, ICSS_BLOCK_SIZE);
>> + if (pkt_block_size > free_blocks) /* out of queue space */
>> + return -ENOBUFS;
>> +
>> + /* calculate end BD address post write */
>> + update_block = write_block + pkt_block_size;
>> +
>> + /* Check for wrap around */
>> + if (update_block >= buffer_desc_count) {
>> + update_block %= buffer_desc_count;
>> + buffer_wrapped = true;
>> + }
>> +
>> + /* OCMC RAM is not cached and write order is not important */
>> + ocmc_ram = (__force void *)emac->prueth->mem[PRUETH_MEM_OCMC].va;
>> + dst_addr = ocmc_ram + txqueue->buffer_offset +
>> + (write_block * ICSS_BLOCK_SIZE);
>> +
>> + /* Copy the data from socket buffer(DRAM) to PRU buffers(OCMC) */
>> + if (buffer_wrapped) { /* wrapped around buffer */
>> + int bytes = (buffer_desc_count - write_block) * ICSS_BLOCK_SIZE;
>> + int remaining;
>> +
>> + /* bytes is integral multiple of ICSS_BLOCK_SIZE but
>> + * entire packet may have fit within the last BD
>> + * if pkt_info.length is not integral multiple of
>> + * ICSS_BLOCK_SIZE
>> + */
>> + if (pktlen < bytes)
>> + bytes = pktlen;
>> +
>> + /* copy non-wrapped part */
>> + memcpy(dst_addr, src_addr, bytes);
>> +
>> + /* copy wrapped part */
>> + src_addr += bytes;
>> + remaining = pktlen - bytes;
>> + dst_addr = ocmc_ram + txqueue->buffer_offset;
>> + memcpy(dst_addr, src_addr, remaining);
>> + } else {
>> + memcpy(dst_addr, src_addr, pktlen);
>> + }
>> +
>> + /* update first buffer descriptor */
>> + wr_buf_desc = (pktlen << PRUETH_BD_LENGTH_SHIFT) &
>> + PRUETH_BD_LENGTH_MASK;
>> + writel(wr_buf_desc, dram + bd_wr_ptr);
>> +
>> + /* update the write pointer in this queue descriptor, the firmware
>> + * polls for this change so this will signal the start of transmission
>> + */
>> + update_wr_ptr = txqueue->buffer_desc_offset + (update_block * BD_SIZE);
>> + writew(update_wr_ptr, &queue_desc->wr_ptr);
>> +
>> + return 0;
>> +}
>
> [...]
>
>> +
>> +/* get packet from queue
>> + * negative for error
>> + */
>
> The comment above seems superfluous and does not seem to follow the
> format of the tx comment which appears to use kdoc style
>

We will address in the next version.

>> +int icssm_emac_rx_packet(struct prueth_emac *emac, u16 *bd_rd_ptr,
>> + struct prueth_packet_info *pkt_info,
>> + const struct prueth_queue_info *rxqueue)
>> +{
>
> [...]
>
>> +
>> + /* the PRU firmware deals mostly in pointers already
>> + * offset into ram, we would like to deal in indexes
>> + * within the queue we are working with for code
>> + * simplicity, calculate this here
>> + */
>> + buffer_desc_count = rxqueue->buffer_desc_end -
>> + rxqueue->buffer_desc_offset;
>> + buffer_desc_count /= BD_SIZE;
>> + buffer_desc_count++;
>> + read_block = (*bd_rd_ptr - rxqueue->buffer_desc_offset) / BD_SIZE;
>> + pkt_block_size = DIV_ROUND_UP(pkt_info->length, ICSS_BLOCK_SIZE);
>> +
>> + /* calculate end BD address post read */
>> + update_block = read_block + pkt_block_size;
>> +
>> + /* Check for wrap around */
>> + if (update_block >= buffer_desc_count) {
>> + update_block %= buffer_desc_count;
>> + if (update_block)
>> + buffer_wrapped = true;
>> + }
>> +
>> + /* calculate new pointer in ram */
>> + *bd_rd_ptr = rxqueue->buffer_desc_offset + (update_block * BD_SIZE);
>
> Seems like there's a lot of repeated math here and in the above
> function. Maybe this can be simplified with a helper function to
> avoid repeating the math in multiple places?
>

We will plan to re-look into common code (more than twice) and create a helper
function and use it.

>> +
>> + /* Pkt len w/ HSR tag removed, If applicable */
>> + actual_pkt_len = pkt_info->length - start_offset;
>> +
>> + /* Allocate a socket buffer for this packet */
>> + skb = netdev_alloc_skb_ip_align(ndev, actual_pkt_len);
>> + if (!skb) {
>> + if (netif_msg_rx_err(emac) && net_ratelimit())
>> + netdev_err(ndev, "failed rx buffer alloc\n");
>> + return -ENOMEM;
>> + }
>> +
>> + dst_addr = skb->data;
>> +
>> + /* OCMC RAM is not cached and read order is not important */
>> + ocmc_ram = (__force void *)emac->prueth->mem[PRUETH_MEM_OCMC].va;
>> +
>> + /* Get the start address of the first buffer from
>> + * the read buffer description
>> + */
>> + src_addr = ocmc_ram + rxqueue->buffer_offset +
>> + (read_block * ICSS_BLOCK_SIZE);
>> + src_addr += start_offset;
>> +
>> + /* Copy the data from PRU buffers(OCMC) to socket buffer(DRAM) */
>> + if (buffer_wrapped) { /* wrapped around buffer */
>> + int bytes = (buffer_desc_count - read_block) * ICSS_BLOCK_SIZE;
>> + int remaining;
>> + /* bytes is integral multiple of ICSS_BLOCK_SIZE but
>> + * entire packet may have fit within the last BD
>> + * if pkt_info.length is not integral multiple of
>> + * ICSS_BLOCK_SIZE
>> + */
>> + if (pkt_info->length < bytes)
>> + bytes = pkt_info->length;
>> +
>> + /* If applicable, account for the HSR tag removed */
>> + bytes -= start_offset;
>> +
>> + /* copy non-wrapped part */
>> + memcpy(dst_addr, src_addr, bytes);
>> +
>> + /* copy wrapped part */
>> + dst_addr += bytes;
>> + remaining = actual_pkt_len - bytes;
>> +
>> + src_addr = ocmc_ram + rxqueue->buffer_offset;
>> + memcpy(dst_addr, src_addr, remaining);
>> + src_addr += remaining;
>> + } else {
>> + memcpy(dst_addr, src_addr, actual_pkt_len);
>> + src_addr += actual_pkt_len;
>> + }
>> +
>> + if (!pkt_info->sv_frame) {
>> + skb_put(skb, actual_pkt_len);
>> +
>> + /* send packet up the stack */
>> + skb->protocol = eth_type_trans(skb, ndev);
>> + local_bh_disable();
>> + netif_receive_skb(skb);
>> + local_bh_enable();
>> + } else {
>> + dev_kfree_skb_any(skb);
>> + }
>> +
>> + /* update stats */
>> + ndev->stats.rx_bytes += actual_pkt_len;
>> + ndev->stats.rx_packets++;
>
> See comment below about atomicity.
>
>> + return 0;
>> +}
>> +
>> +/**
>> + * icssm_emac_rx_thread - EMAC Rx interrupt thread handler
>> + * @irq: interrupt number
>> + * @dev_id: pointer to net_device
>> + *
>> + * EMAC Rx Interrupt thread handler - function to process the rx frames in a
>> + * irq thread function. There is only limited buffer at the ingress to
>> + * queue the frames. As the frames are to be emptied as quickly as
>> + * possible to avoid overflow, irq thread is necessary. Current implementation
>> + * based on NAPI poll results in packet loss due to overflow at
>> + * the ingress queues. Industrial use case requires loss free packet
>> + * processing. Tests shows that with threaded irq based processing,
>> + * no overflow happens when receiving at ~92Mbps for MTU sized frames and thus
>> + * meet the requirement for industrial use case.
>
> That's interesting. Any idea why this is the case? Is there not
> enough CPU for softirq/NAPI processing to run or something? I
> suppose I'd imagine that NAPI would run and if data is arriving fast
> enough, the NAPI would be added to the repoll list and processed
> later.
>
> So I guess either there isn't enough CPU or the ingress queues don't
> have many descriptors or something like that ?
>

This is due to combination of both limited number of buffer descriptors
(memory constraints) and also not having enough CPU.

>> + *
>> + * Return: interrupt handled condition
>> + */
>> +static irqreturn_t icssm_emac_rx_thread(int irq, void *dev_id)
>> +{
>> + struct net_device *ndev = (struct net_device *)dev_id;
>> + struct prueth_emac *emac = netdev_priv(ndev);
>> + struct prueth_queue_desc __iomem *queue_desc;
>> + const struct prueth_queue_info *rxqueue;
>> + struct prueth *prueth = emac->prueth;
>> + struct net_device_stats *ndevstats;
>> + struct prueth_packet_info pkt_info;
>> + int start_queue, end_queue;
>> + void __iomem *shared_ram;
>> + u16 bd_rd_ptr, bd_wr_ptr;
>> + u16 update_rd_ptr;
>> + u8 overflow_cnt;
>> + u32 rd_buf_desc;
>> + int used = 0;
>> + int i, ret;
>> +
>> + ndevstats = &emac->ndev->stats;
>
> FWIW the docs in include/linux/netdevice.h say:
>
> /**
> ...
> * @stats: Statistics struct, which was left as a legacy, use
> * rtnl_link_stats64 instead
> ...
> */
> struct net_device {
> ...
> struct net_device_stats stats; /* not used by modern drivers */
> ...
> };
>
> perhaps consider using rtnl_link_stats64 as suggested instead?
>
>> + shared_ram = emac->prueth->mem[PRUETH_MEM_SHARED_RAM].va;
>> +
>> + start_queue = emac->rx_queue_start;
>> + end_queue = emac->rx_queue_end;
>> +retry:
>> + /* search host queues for packets */
>> + for (i = start_queue; i <= end_queue; i++) {
>> + queue_desc = emac->rx_queue_descs + i;
>> + rxqueue = &queue_infos[PRUETH_PORT_HOST][i];
>> +
>> + overflow_cnt = readb(&queue_desc->overflow_cnt);
>> + if (overflow_cnt > 0) {
>> + emac->ndev->stats.rx_over_errors += overflow_cnt;
>> + /* reset to zero */
>> + writeb(0, &queue_desc->overflow_cnt);
>> + }
>> +
>> + bd_rd_ptr = readw(&queue_desc->rd_ptr);
>> + bd_wr_ptr = readw(&queue_desc->wr_ptr);
>> +
>> + /* while packets are available in this queue */
>> + while (bd_rd_ptr != bd_wr_ptr) {
>> + /* get packet info from the read buffer descriptor */
>> + rd_buf_desc = readl(shared_ram + bd_rd_ptr);
>> + icssm_parse_packet_info(prueth, rd_buf_desc, &pkt_info);
>> +
>> + if (pkt_info.length <= 0) {
>> + /* a packet length of zero will cause us to
>> + * never move the read pointer ahead, locking
>> + * the driver, so we manually have to move it
>> + * to the write pointer, discarding all
>> + * remaining packets in this queue. This should
>> + * never happen.
>> + */
>> + update_rd_ptr = bd_wr_ptr;
>> + ndevstats->rx_length_errors++;
>
> See question below.
>
>> + } else if (pkt_info.length > EMAC_MAX_FRM_SUPPORT) {
>> + /* if the packet is too large we skip it but we
>> + * still need to move the read pointer ahead
>> + * and assume something is wrong with the read
>> + * pointer as the firmware should be filtering
>> + * these packets
>> + */
>> + update_rd_ptr = bd_wr_ptr;
>> + ndevstats->rx_length_errors++;
>
> in netdevice.h it says:
>
> * struct net_device_stats* (*ndo_get_stats)(struct net_device *dev);
> * Called when a user wants to get the network device usage
> * statistics. Drivers must do one of the following:
> * 1. Define @ndo_get_stats64 to fill in a zero-initialised
> * rtnl_link_stats64 structure passed by the caller.
> * 2. Define @ndo_get_stats to update a net_device_stats structure
> * (which should normally be dev->stats) and return a pointer to
> * it. The structure may be changed asynchronously only if each
> * field is written atomically.
> * 3. Update dev->stats asynchronously and atomically, and define
> * neither operation.
>
> I didn't look in the other patches to see if ndo_get_stats is
> defined or not, but are these increments atomic?

This module maintain 32 bit statistics inside PRU firmware. we will
check the feasibility of using rtnl_link_stats64 and make appropriate
changes as per your suggestion in next version.

Thanks & Best Regards,
Basharath