linux-kernel - Re: [PATCH v14 8/8] soc: amd: Add support for AMD Pensando SoC Controller

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Message-ID: <20230523021256.61690-1-blarson@amd.com>
Date:   Mon, 22 May 2023 19:12:56 -0700
From:   Brad Larson <blarson@....com>
To:     <andy.shevchenko@...il.com>
CC:     <adrian.hunter@...el.com>, <alcooperx@...il.com>, <arnd@...db.de>,
        <blarson@....com>, <brendan.higgins@...ux.dev>,
        <briannorris@...omium.org>, <broonie@...nel.org>,
        <catalin.marinas@....com>, <conor+dt@...nel.org>,
        <davidgow@...gle.com>, <devicetree@...r.kernel.org>,
        <fancer.lancer@...il.com>, <gerg@...ux-m68k.org>,
        <gsomlo@...il.com>, <hal.feng@...rfivetech.com>,
        <hasegawa-hitomi@...itsu.com>, <j.neuschaefer@....net>,
        <joel@....id.au>, <kernel@...il.dk>, <krzk@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <lee.jones@...aro.org>,
        <lee@...nel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-mmc@...r.kernel.org>,
        <linux-spi@...r.kernel.org>, <p.zabel@...gutronix.de>,
        <rdunlap@...radead.org>, <robh+dt@...nel.org>,
        <samuel@...lland.org>, <skhan@...uxfoundation.org>,
        <suravee.suthikulpanit@....com>, <thomas.lendacky@....com>,
        <tonyhuang.sunplus@...il.com>, <ulf.hansson@...aro.org>,
        <vaishnav.a@...com>, <walker.chen@...rfivetech.com>,
        <will@...nel.org>, <zhuyinbo@...ngson.cn>
Subject: Re: [PATCH v14 8/8] soc: amd: Add support for AMD Pensando SoC Controller

Hi Andy,

On Tue, May 16, 2023 at 00:05:32 Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> On Mon, May 15, 2023 at 9:18 PM Brad Larson <blarson@....com> wrote:
>>
>> The Pensando SoC controller is a SPI connected companion device
>> that is present in all Pensando SoC board designs.  The essential
>> board management registers are accessed on chip select 0 with
>> board mgmt IO support accessed using additional chip selects.
>
> ...
>
>> +#include <linux/cdev.h>
>> +#include <linux/device.h>
>> +#include <linux/err.h>
>> +#include <linux/init.h>
>> +#include <linux/mod_devicetable.h>
>> +#include <linux/module.h>
>> +#include <linux/mutex.h>
>
>> +#include <linux/of.h>
>
> Unneeded inclusion.

Removed

>> +#include <linux/reset-controller.h>
>> +#include <linux/spi/spi.h>
>
> ...
>
>
>> +       u8 tx_buf[PENCTRL_MAX_MSG_LEN];
>> +       u8 rx_buf[PENCTRL_MAX_MSG_LEN];
>
> Does it need to be DMA-capable?

Doesn't need to be DMA-capable

> ...
>
>> +       spi->chip_select = current_cs;
>> +       spi->cs_gpiod = spi->controller->cs_gpiods[current_cs];
>
> Nowadays these require API calls instead of direct assignments.

Changed to:
	spi_set_csgpiod(spi, 0, spi->controller->cs_gpiods[current_cs]);

> ...
>
>> +static int penctrl_release(struct inode *inode, struct file *filp)
>> +{
>> +       filp->private_data = NULL;
>> +       return 0;
>> +}
>
> Is it possible to unload the module without releasing the device node?

If the refcount is not zero the kernel prevents the module from being unloaded.

> ...
>
>> +       u8 txbuf[3];
>> +       u8 rxbuf[1];
>
> Same question about DMA.

Not DMA-capable

> ...
>
>> +       ret = spi_sync(spi, &m);
>
>> +       if (ret == 0)
>> +               *val = rxbuf[0];
>> +
>> +       return ret;
>
> Can also be written in more usual way:
>
>  if (ret)
>    return ret;
>  ...
>  return 0;

Yes, changed to:
        ret = spi_sync(spi, &m);
        if (ret)
                return ret;

        *val = rxbuf[0];
        return 0;

> ...
>
>> +       u8 txbuf[4];
>
> DMA?

Not DMA-capable

> ...
>
>> +       spi->chip_select = 0;
>> +       spi->cs_gpiod = spi->controller->cs_gpiods[0];
>
> Setter APIs.

Changed to:
	spi_set_csgpiod(spi, 0, spi->controller->cs_gpiods[0]);

>
> ...
>
>> +       spi->chip_select = 0;
>> +       spi->cs_gpiod = spi->controller->cs_gpiods[0];
>
> Ditto.

Changed to:
	spi_set_csgpiod(spi, 0, spi->controller->cs_gpiods[0]);

>> +       ret = device_property_read_u32(spi->dev.parent, "num-cs", &num_cs);
>> +       if (ret)
>> +               return dev_err_probe(&spi->dev, ret,
>> +                                    "number of chip-selects not defined\n");
>
> Hmm... Shouldn't SPI core take care of this in a generic way? Yes, I
> understand that you need the number for the allocation, but I would
> expect something like spi_fw_get_num_cs() to exist (seems not?).
>

No need to look into the parent node, changed to this:

        num_cs = spi->controller->num_chipselect;

> ...
>
>> +       penctrl->rcdev.of_node = spi->dev.of_node;
>
> Use device_set_node(). It helps to modify the data types beneath.

Added:
	device_set_node(penctrl->rcdev.dev, dev_fwnode(&spi->dev));

Regards,
Brad