linux-kernel - Re: [PATCH 1/1] misc: mrvl-dpi: add octeontx3 dpi driver

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Date: Wed, 14 Feb 2024 12:22:53 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Vamsi Attunuru" <vattunuru@...vell.com>,
 "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] misc: mrvl-dpi: add octeontx3 dpi driver

On Wed, Feb 14, 2024, at 04:55, Vamsi Attunuru wrote:
> Adds PCIe PF driver for OcteonTx3 DPI PF device which initializes DPI
> DMA hardware's global configuration and enables PF-VF mbox channels
> which can be used by it's VF devices. This DPI PF driver handles only
> the resource configuration requests from VFs and it does not have any
> data movement functionality.
>
> Signed-off-by: Vamsi Attunuru <vattunuru@...vell.com>

This looks incomplete, as there is no apparent interface to
actually use the driver from either userspace or kernel. I
understand that you want to merge this one step at a time,
but please try to at least point out how this is intended
to be used, or post it together with an (in-kernel) user
if you plan to upstream that.

Is this used for anything other than networking? If not,
maybe it should be part of drivers/net/ instead of
drivers/misc.

A few more things that Greg hasn't already commented on:

> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index 4fb291f0bf7c..3142fdb1b4c0 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -574,6 +574,16 @@ config NSM
>  	  To compile this driver as a module, choose M here.
>  	  The module will be called nsm.
> 
> +config MARVELL_OCTEONTX3_DPI
> +	tristate "OcteonTX3 DPI driver"

Is OcteonTX3 an actual product name? I thought the follow-up
to OcteonTX2 (cn9[268]xx) was the OCTEON 10 line. Or is
this a follow-up to the Marvell Armada (cn91xx) line?

> +static void dpi_poll_pfvf_mbox(struct dpipf *dpi)
> +{
> +	u64 reg;
> +	u32 vf;
> +
> +	reg = dpi_reg_read(dpi, DPI_MBOX_VF_PF_INT);
> +	if (reg) {
> +		for (vf = 0; vf < DPI_MAX_VFS; vf++) {
> +			if (!(reg & (0x1UL << vf)))
> +				continue;
> +
> +			if (!dpi->mbox[vf]) {
> +				dev_err(&dpi->pdev->dev, "bad mbox vf %d\n", vf);
> +				continue;
> +			}
> +
> +			schedule_work(&dpi->mbox[vf]->wk.work);
> +		}
> +
> +		if (reg)
> +			dpi_reg_write(dpi, DPI_MBOX_VF_PF_INT, reg);
> +	}
> +}
> +
> +static irqreturn_t dpi_mbox_intr_handler(int irq, void *data)
> +{
> +	struct dpipf *dpi = data;
> +
> +	dpi_poll_pfvf_mbox(dpi);
> +
> +	return IRQ_HANDLED;
> +}

Have you considered using the drivers/mailbox framework for
the mailbox portion?


> +static void dpi_pfvf_mbox_work(struct work_struct *work)
> +{
> +	struct dpi_pfvf_mbox_wk *wk = container_of(work, struct 
> dpi_pfvf_mbox_wk, work);
> +	union dpi_mbox_message_t msg = { 0 };
> +	struct dpi_mbox *mbox = NULL;
> +	struct dpipf_vf *dpivf;
> +	struct dpipf *dpi;
> +	int vf_id;
> +
> +	mbox = (struct dpi_mbox *)wk->ctxptr;
> +	dpi = (struct dpipf *)mbox->pf;

Can these pointers be strictly typed instead of casting
from a void*?

> +static int dpi_pfvf_mbox_setup(struct dpipf *dpi)
> +{
> +	int vf;
> +
> +	for (vf = 0; vf < DPI_MAX_VFS; vf++) {
> +		dpi->mbox[vf] = vzalloc(sizeof(*dpi->mbox[vf]));
> +

dpi->mbox[vf] does not look excessively large, so I think
kzalloc() is better than vzalloc() here.

> +module_init(dpi_init_module);
> +module_exit(dpi_cleanup_module);
> +MODULE_DEVICE_TABLE(pci, dpi_id_table);
> +MODULE_AUTHOR("Marvell International Ltd.");
> +MODULE_DESCRIPTION(DPI_DRV_STRING);
> +MODULE_LICENSE("GPL");
> +MODULE_VERSION(DPI_DRV_VERSION);

Please remove the DPI_DRV_STRING and DPI_DRV_VERSION macros,
they prevent grepping for the strings.

> diff --git a/drivers/misc/mrvl-dpi/dpi.h b/drivers/misc/mrvl-dpi/dpi.h
> new file mode 100644
> index 000000000000..99ebe6bbe577
> --- /dev/null
> +++ b/drivers/misc/mrvl-dpi/dpi.h
> @@ -0,0 +1,232 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Marvell OcteonTx3 DPI driver
> + *
> + * Copyright (C) 2024 Marvell International Ltd.
> + */
> +
> +#ifndef __DPI_H__
> +#define __DPI_H__

I see no need for a separate header file if there is no other
driver including it, so just merge this all into the .c file.

> +union dpi_mbox_message_t {
> +	uint64_t u[2];
> +	struct dpi_mbox_message_s {
> +		/* VF ID to configure */
> +		uint64_t vfid           :8;
> +		/* Command code */
> +		uint64_t cmd            :4;
> +		/* Command buffer size in 8-byte words */
> +		uint64_t csize          :14;
> +		/* aura of the command buffer */
> +		uint64_t aura           :20;
> +		/* SSO PF function */
> +		uint64_t sso_pf_func    :16;
> +		/* NPA PF function */
> +		uint64_t npa_pf_func    :16;
> +		/* Work queue completion status enable */
> +		uint64_t wqecs		:1;
> +		/* Work queue completion status byte offset */
> +		uint64_t wqecsoff	:7;
> +	} s __packed;
> +};

Is this a hardware structure? If it is, you probably don't
want to use bit fields here, even in the best case that
is a bug that prevents you from using the driver in
big-endian mode.

I also see that there are only 86 bits defined, and one
field crosses a 64-bit boundary, which feels odd.

    Arnd