linux-kernel - Re: [RFC PATCH 5/8] qaic: Implement data path

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Message-ID: <CAK8P3a34ks226S9UJMfCNdY3KWiBS+vscYdKwLW7wkLj0H_4Cw@mail.gmail.com>
Date:   Thu, 14 May 2020 23:36:27 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Jeffrey Hugo <jhugo@...eaurora.org>
Cc:     gregkh <gregkh@...uxfoundation.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        wufan@...eaurora.org, pratanan@...eaurora.org,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 5/8] qaic: Implement data path

On Thu, May 14, 2020 at 4:09 PM Jeffrey Hugo <jhugo@...eaurora.org> wrote:
>
> +struct dbc_req { /* everything must be little endian encoded */

Instead of the comment, I suppose you want to use __le16 and __le32
types and let sparse check that you got it right.

> +       u16     req_id;
> +       u8      seq_id;
> +       u8      cmd;
> +       u32     resv;
> +       u64     src_addr;
> +       u64     dest_addr;
> +       u32     len;
> +       u32     resv2;
> +       u64     db_addr; /* doorbell address */
> +       u8      db_len; /* not a raw value, special encoding */
> +       u8      resv3;
> +       u16     resv4;
> +       u32     db_data;
> +       u32     sem_cmd0;
> +       u32     sem_cmd1;
> +       u32     sem_cmd2;
> +       u32     sem_cmd3;
> +} __packed;

All members are naturally aligned, so better drop the __packed
annotation get better code, unless the structure itself is
at an unaligned offset in memory.

> +struct dbc_rsp { /* everything must be little endian encoded */
> +       u16     req_id;
> +       u16     status;
> +} __packed;

Same here.

> +       init_completion(&mem->xfer_done);
> +       list_add_tail(&mem->list, &dbc->xfer_list);
> +       tail = (tail + mem->nents) % dbc->nelem;
> +       __raw_writel(cpu_to_le32(tail), dbc->dbc_base + REQTP_OFF);

What is this __raw accessor for? This generally results in non-portable
code that should be replaced with writel() or something specific to
the bus on the architecture you deal with.

> +       spin_lock_irqsave(&qdev->dbc[exec->dbc_id].xfer_lock, flags);
> +       req_id = qdev->dbc[exec->dbc_id].next_req_id++;
> +       queued = mem->queued;
> +       mem->queued = true;
> +       spin_unlock_irqrestore(&qdev->dbc[exec->dbc_id].xfer_lock, flags);

No need for 'irqsave' locks when you know that interrupts are enabled.

> +       head = le32_to_cpu(__raw_readl(dbc->dbc_base + RSPHP_OFF));
> +       tail = le32_to_cpu(__raw_readl(dbc->dbc_base + RSPTP_OFF));

More __raw accessors to replace.

> +       case QAIC_IOCTL_MEM_NR:
> +               if (_IOC_DIR(cmd) != (_IOC_READ | _IOC_WRITE) ||
> +                   _IOC_SIZE(cmd) != sizeof(struct qaic_mem_req)) {
> +                       ret = -EINVAL;
> +                       break;

This looks like a very verbose way to check 'cmd' against a known
constant. Why not use 'switch (cmd)' like all other drivers?

      Arnd