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Date: Thu, 20 Jan 2022 16:20:24 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Jan Dabros <jsd@...ihalf.com>
Cc: linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
jarkko.nikula@...ux.intel.com, mika.westerberg@...ux.intel.com,
hdegoede@...hat.com, wsa@...nel.org, rrangel@...omium.org,
mw@...ihalf.com, jaz@...ihalf.com, upstream@...ihalf.com
Subject: Re: [PATCH 2/2] i2c: designware: Add AMD PSP I2C bus support
On Thu, Jan 20, 2022 at 01:16:21AM +0100, Jan Dabros wrote:
> Implement an I2C controller sharing mechanism between the host (kernel)
> and PSP co-processor on some platforms equipped with AMD Cezanne SoC.
>
> On these platforms we need to implement "software" i2c arbitration.
> Default arbitration owner is PSP and kernel asks for acquire as well
> as inform about release of the i2c bus via mailbox mechanism.
>
> +---------+
> <- ACQUIRE | |
> +---------| CPU |\
> | | | \ +----------+ SDA
> | +---------+ \ | |-------
> MAILBOX +--> | I2C-DW | SCL
> | +---------+ | |-------
> | | | +----------+
> +---------| PSP |
> <- ACK | |
> +---------+
>
> +---------+
> <- RELEASE | |
> +---------| CPU |
> | | | +----------+ SDA
> | +---------+ | |-------
> MAILBOX +--> | I2C-DW | SCL
> | +---------+ / | |-------
> | | | / +----------+
> +---------| PSP |/
> <- ACK | |
> +---------+
>
> The solution is similar to i2c-designware-baytrail.c implementation, where
> we are using a generic i2c-designware-* driver with a small "wrapper".
>
> In contrary to baytrail semaphore implementation, beside internal
> acquire_lock() and release_lock() methods we are also applying quirks to
> lock_bus() and unlock_bus() global adapter methods. With this in place
> all i2c clients drivers may lock i2c bus for a desired number of i2c
> transactions (e.g. write-wait-read) without being aware of that such bus
> is shared with another entity.
>
> Modify i2c_dw_probe_lock_support() to select correct semaphore
> implementation at runtime, since now we have more than one available.
>
> Configure new matching ACPI ID "AMDI0019" and register
> ARBITRATION_SEMAPHORE flag in order to distinguish setup with PSP
> arbitration.
> Add new entry in MAINTAINERS file to cover new module.
It's confusing. You added yourself as a reviewer for I2C DesignWare driver,
which is great, but not described in the commit message.
...
> { "AMD0020", APD_ADDR(cz_uart_desc) },
> { "AMDI0020", APD_ADDR(cz_uart_desc) },
> { "AMDI0022", APD_ADDR(cz_uart_desc) },
> + { "AMDI0019", APD_ADDR(wt_i2c_desc) },
This addition adds more chaos in the ordering (the group of AMDI should be
after AMD as far as I can see here). Can you order the entries by IDs?
> { "AMD0030", },
> { "AMD0040", APD_ADDR(fch_misc_desc)},
...
> +#include <asm/msr.h>
Usually linux/* followed by asm/*.
> +#include <linux/i2c.h>
> +#include <linux/psp-sev.h>
types.h?
...
> +union psp_req_buffer_hdr {
> + struct {
> + u32 total_size;
> + u32 status;
> + } __packed;
What does packet bring you here?
> + u64 hdr_val;
And why does this not have the same alignment since it's also part of
the union?
> +};
> +
> +enum psp_i2c_req_type {
> + PSP_I2C_REQ_ACQUIRE,
> + PSP_I2C_REQ_RELEASE,
> + PSP_I2C_REQ_MAX,
Is MAX a terminator or not?
If former, no comma.
> +};
> +
> +struct psp_i2c_req {
> + union psp_req_buffer_hdr hdr;
> + enum psp_i2c_req_type type;
> +} __packed __aligned(32);
Can you explain, what this means and how it's supposed to work?
> +union psp_mbox_cmd_reg {
> + struct psp_mbox_cmd_fields {
> + u16 mbox_status;
> + u8 mbox_cmd;
> + u8 reserved:6;
> + u8 recovery:1;
> + u8 ready:1;
> + } __packed fields;
So, what is the __packed purpose here?
> + u32 val;
> +};
> +
> +struct psp_mbox {
> + union psp_mbox_cmd_reg fields;
> + uintptr_t i2c_req_addr;
> +} __packed;
...
> +static int psp_mbox_probe(void)
> +{
> + unsigned long mbox_addr;
> +
> + if (psp_get_mbox_addr(&mbox_addr))
> + return -1;
Use error code.
> + mbox_iomem = ioremap(mbox_addr, sizeof(struct psp_mbox));
> + if (!mbox_iomem)
> + return -ENOMEM;
> +
> + return 0;
> +}
...
> + union psp_mbox_cmd_reg tmp = {0};
> + tmp.val = readl(&mbox->fields.val);
> + return !!tmp.fields.recovery;
OK, I understood the purpose of unions, no, please use bitfield.h APIs.
...
> + struct psp_mbox *mbox = (struct psp_mbox *)mbox_iomem;
Heck, no!
...
> + /* Fill address of command-response buffer */
> + writeq((uintptr_t)__psp_pa((void *)req), &mbox->i2c_req_addr);
What does this voodoo mean?!
...
> + start = jiffies;
> + do {
> + if (psp_send_cmd(req)) {
> + ret = -EIO;
> + goto cleanup;
> + }
> +
> + status = check_i2c_req_sts(req);
> + if (!status) {
> + dev_dbg(psp_i2c_dev, "Request accepted by PSP after %ums\n",
> + jiffies_to_msecs(jiffies - start));
> + ret = 0;
> + goto cleanup;
> + } else if (status == -EBUSY) {
> + retry_cnt--;
> + } else {
> + ret = -EIO;
> + goto cleanup;
> + };
> +
> + /* IF EBUSY, give PSP time to finish its i2c activities */
> + mdelay(PSP_I2C_REQ_RETRY_DELAY_MSEC);
> + } while (retry_cnt);
NIH iopoll.h API(s).
> + ret = -ETIMEDOUT;
...
> + status = psp_send_i2c_req(PSP_I2C_REQ_ACQUIRE);
> + if (!status) {
Handle errors first.
...
> + goto cleanup;
> + } else if (status == -ETIMEDOUT) {
In this case it's redundant 'else'.
...
> + /* Send a release command to PSP */
> + status = psp_send_i2c_req(PSP_I2C_REQ_RELEASE);
> + if (!status) {
> + dev_dbg(psp_i2c_dev, "PSP semaphore held for %ums\n",
> + jiffies_to_msecs(jiffies - psp_i2c_sem_acquired));
> + goto cleanup;
> + } else if (status == -ETIMEDOUT) {
> + dev_err(psp_i2c_dev, "Timed out waiting for PSP to acquire I2C bus\n");
> + } else {
> + dev_err(psp_i2c_dev, "PSP communication error\n");
> + }
As per above comments.
...
> + int ret;
> +
> + ret = rt_mutex_trylock(&adapter->bus_lock);
> + if (!ret)
if (ret)
...
> + psp_acquire_i2c_bus();
> +
> + return ret;
...
> + /* Allow to bind only one instance of a driver */
> + if (!psp_i2c_dev)
> + psp_i2c_dev = dev->dev;
> + else
> + return -EEXIST;
As per above.
...
> + if (psp_mbox_probe())
> + return -EIO;
Why error code is hidden?
...
> + /*
> + * Install global locking callbacks for adapter as well as internal i2c
> + * controller locks
Missed period.
> + */
...
> { "AMD0010", ACCESS_INTR_MASK },
> { "AMDI0010", ACCESS_INTR_MASK },
> { "AMDI0510", 0 },
> + { "AMDI0019", ACCESS_INTR_MASK | ARBITRATION_SEMAPHORE },
It's not in order.
...
> +static const struct i2c_dw_semaphore_callbacks i2c_dw_semaphore_cb_table[] = {
> +#ifdef CONFIG_I2C_DESIGNWARE_BAYTRAIL
> + {
> + .probe = i2c_dw_baytrail_probe_lock_support,
> + .remove = NULL,
See below.
> + },
> +#endif
> +#ifdef CONFIG_I2C_DESIGNWARE_AMDPSP
> + {
> + .probe = i2c_dw_amdpsp_probe_lock_support,
> + .remove = i2c_dw_amdpsp_remove_lock_support,
> + },
> +#endif
> + {
> + .probe = NULL,
> + .remove = NULL,
> + },
First of all, it should be terminating entry, so no comma.
On top of that, no need to assign 0/NULL to static variables.
So here, it will become as simple as
{}
> +};
...
> +static int i2c_dw_probe_lock_support(struct dw_i2c_dev *dev)
> +{
> + int ret;
> + int i;
> +
> + dev->semaphore_idx = -1;
> +
> + for (i = 0; i < ARRAY_SIZE(i2c_dw_semaphore_cb_table); i++) {
> + if (!i2c_dw_semaphore_cb_table[i].probe)
> + continue;
Huh?
> + }
> +
> + return 0;
> +}
--
With Best Regards,
Andy Shevchenko
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