Hi Andy,
śr., 2 lut 2022 o 17:16 Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> napisał(a):
>
> On Wed, Feb 02, 2022 at 03:43:02PM +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 myself as a reviewer for I2C DesignWare in order to help with reviewing
> > and testing possible changes touching new i2c-designware-amdpsp.c module.
>
> Side note, please start a new email thread for new version of the series.
Sure, will do so starting with v4.
>
> Looks good enough to me, although a few minor comments below.
> Up to you to address them now or later.
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Thanks a lot! I will address your comments and send v4.
>
> > Signed-off-by: Jan Dabros <jsd@xxxxxxxxxxxx>
(...)
> > --- /dev/null
> > +++ b/drivers/i2c/busses/i2c-designware-amdpsp.c
> > @@ -0,0 +1,389 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include <linux/bitfield.h>
>
> IIRC this does not guarantee bits.h inclusion.
That is correct. There is a comment in bitfield.h with example of
GENMASK usage, but bits.h isn't actually included there.
>
> > +#include <linux/i2c.h>
> > +#include <linux/io-64-nonatomic-lo-hi.h>
> > +#include <linux/psp-sev.h>
> > +#include <linux/types.h>
> > +
> > +#include <asm/msr.h>
> > +
> > +#include "i2c-designware-core.h"
> > +
> > +#define MSR_AMD_PSP_ADDR 0xc00110a2
> > +#define PSP_MBOX_OFFSET 0x10570
> > +#define PSP_CMD_TIMEOUT_MS 500
> > +
> > +#define PSP_I2C_REQ_BUS_CMD 0x64
> > +#define PSP_I2C_REQ_RETRY_CNT 10
> > +#define PSP_I2C_REQ_RETRY_DELAY_USEC (50 * 1000)
>
> _US is enough and possibly (50 * USEC_PER_MSEC).
ACK.
>
> > +#define PSP_I2C_REQ_STS_OK 0x0
> > +#define PSP_I2C_REQ_STS_BUS_BUSY 0x1
> > +#define PSP_I2C_REQ_STS_INV_PARAM 0x3
> > +
> > +#define PSP_MBOX_FIELDS_STS GENMASK(15, 0)
> > +#define PSP_MBOX_FIELDS_CMD GENMASK(23, 16)
> > +#define PSP_MBOX_FIELDS_RESERVED GENMASK(29, 24)
> > +#define PSP_MBOX_FIELDS_RECOVERY BIT(30)
> > +#define PSP_MBOX_FIELDS_READY BIT(31)
> > +
> > +struct psp_req_buffer_hdr {
> > + u32 total_size;
> > + u32 status;
> > +};
> > +
> > +enum psp_i2c_req_type {
> > + PSP_I2C_REQ_ACQUIRE,
> > + PSP_I2C_REQ_RELEASE,
> > + PSP_I2C_REQ_MAX
> > +};
> > +
> > +struct psp_i2c_req {
> > + struct psp_req_buffer_hdr hdr;
> > + enum psp_i2c_req_type type;
> > +} __aligned(32);
>
> I forgot if this alignment is requirement due to DMA or so?
> We may use ____cacheline_aligned in such case.
I used some old code as a reference - this structure is mapped by PSP,
thus alignment applied here. I'm checking this with AMD whether it is
really needed or at least can be somehow limited - still waiting for
their response.
I propose to left this as is right now and eventually remove or make
more liberal in the future.
>
> > +struct psp_mbox {
> > + u32 cmd_fields;
> > + u64 i2c_req_addr;
> > +} __packed;
> > +
> > +static DEFINE_MUTEX(psp_i2c_access_mutex);
> > +static unsigned long psp_i2c_sem_acquired;
> > +static void __iomem *mbox_iomem;
> > +static u32 psp_i2c_access_count;
> > +static bool psp_i2c_mbox_fail;
> > +static struct device *psp_i2c_dev;
> > +
> > +/*
> > + * Implementation of PSP-x86 i2c-arbitration mailbox introduced for AMD Cezanne
> > + * family of SoCs.
> > + */
> > +
> > +static int psp_get_mbox_addr(unsigned long *mbox_addr)
> > +{
> > + unsigned long long psp_mmio;
> > +
> > + if (rdmsrl_safe(MSR_AMD_PSP_ADDR, &psp_mmio))
> > + return -EIO;
> > +
> > + *mbox_addr = (unsigned long)(psp_mmio + PSP_MBOX_OFFSET);
> > +
> > + return 0;
> > +}
> > +
> > +static int psp_mbox_probe(void)
> > +{
> > + unsigned long mbox_addr;
> > + int ret;
> > +
> > + ret = psp_get_mbox_addr(&mbox_addr);
> > + if (ret)
> > + return ret;
> > +
> > + mbox_iomem = ioremap(mbox_addr, sizeof(struct psp_mbox));
> > + if (!mbox_iomem)
> > + return -ENOMEM;
> > +
> > + return 0;
> > +}
> > +
> > +
> > +/* Recovery field should be equal 0 to start sending commands */
> > +static int psp_check_mbox_recovery(struct psp_mbox __iomem *mbox)
> > +{
> > + u32 tmp;
> > +
> > + tmp = readl(&mbox->cmd_fields);
> > +
> > + return FIELD_GET(PSP_MBOX_FIELDS_RECOVERY, tmp);
> > +}
> > +
> > +static int psp_wait_cmd(struct psp_mbox __iomem *mbox)
> > +{
> > + u32 tmp, expected;
> > +
> > + /* Expect mbox_cmd to be cleared and ready bit to be set by PSP */
> > + expected = FIELD_PREP(PSP_MBOX_FIELDS_READY, 1);
> > +
> > + return readl_poll_timeout(&mbox->cmd_fields, tmp, (tmp == expected),
> > + 0, 1000 * PSP_CMD_TIMEOUT_MS);
>
> 0?!
Yes, we are checking for readiness of PSP mailbox in a tight loop. We
would like to proceed further quickly as soon as this bit is set.
Actually checking this twice per every ACQUIRE&RELEASE - once before
sending command (to check whether PSP is ready to accept requests) and
second time after sending it. Do you think we should increase
@sleep_us value?
>
> > +}
> > +
> > +/* Status equal to 0 means that PSP succeed processing command */
> > +static int psp_check_mbox_sts(struct psp_mbox __iomem *mbox)
>
> static u32 ...
>
> So reader will know it won't return error codes.
ACK/
>
> > +{
> > + u32 cmd_reg;
> > +
> > + cmd_reg = readl(&mbox->cmd_fields);
> > +
> > + return FIELD_GET(PSP_MBOX_FIELDS_STS, cmd_reg);
> > +}
> > +
> > +static int psp_send_cmd(struct psp_i2c_req *req)
> > +{
> > + struct psp_mbox __iomem *mbox = mbox_iomem;
> > + phys_addr_t req_addr;
> > + u32 cmd_reg;
> > +
> > + if (psp_check_mbox_recovery(mbox))
> > + return -EIO;
> > +
> > + if (psp_wait_cmd(mbox))
> > + return -EBUSY;
> > +
> > + /*
> > + * Fill mailbox with address of command-response buffer, which will be
> > + * used for sending i2c requests as well as reading status returned by
> > + * PSP. Use physical address of buffer, since PSP will map this region.
> > + */
> > + req_addr = __psp_pa((void *)req);
> > + writeq(req_addr, &mbox->i2c_req_addr);
> > +
> > + /* Write command register to trigger processing */
> > + cmd_reg = FIELD_PREP(PSP_MBOX_FIELDS_CMD, PSP_I2C_REQ_BUS_CMD);
> > + writel(cmd_reg, &mbox->cmd_fields);
> > +
> > + if (psp_wait_cmd(mbox))
> > + return -ETIMEDOUT;
> > +
> > + if (psp_check_mbox_sts(mbox))
> > + return -EIO;
> > +
> > + return 0;
> > +}
> > +
> > +/* Helper to verify status returned by PSP */
> > +static int check_i2c_req_sts(struct psp_i2c_req *req)
> > +{
> > + int status;
> > +
> > + status = readl(&req->hdr.status);
> > +
> > + switch (status) {
> > + case PSP_I2C_REQ_STS_OK:
> > + return 0;
> > + case PSP_I2C_REQ_STS_BUS_BUSY:
> > + return -EBUSY;
> > + case PSP_I2C_REQ_STS_INV_PARAM:
> > + default:
> > + return -EIO;
> > + };
> > +}
> > +
> > +static int psp_send_check_i2c_req(struct psp_i2c_req *req)
> > +{
> > + /*
> > + * Errors in x86-PSP i2c-arbitration protocol may occur at two levels:
> > + * 1. mailbox communication - PSP is not operational or some IO errors
> > + * with basic communication had happened;
> > + * 2. i2c-requests - PSP refuses to grant i2c arbitration to x86 for too
> > + * long.
> > + * In order to distinguish between these two in error handling code, all
> > + * errors on the first level (returned by psp_send_cmd) are shadowed by
> > + * -EIO.
> > + */
> > + if (psp_send_cmd(req))
> > + return -EIO;
> > +
> > + return check_i2c_req_sts(req);
> > +}
> > +
> > +static int psp_send_i2c_req(enum psp_i2c_req_type i2c_req_type)
> > +{
> > + struct psp_i2c_req *req;
> > + unsigned long start;
> > + int status, ret;
> > +
> > + /* Allocate command-response buffer */
> > + req = kzalloc(sizeof(*req), GFP_KERNEL);
> > + if (!req)
> > + return -ENOMEM;
> > +
> > + req->hdr.total_size = sizeof(*req);
> > + req->type = i2c_req_type;
> > +
> > + start = jiffies;
> > + ret = read_poll_timeout(psp_send_check_i2c_req, status,
> > + (status != -EBUSY),
> > + PSP_I2C_REQ_RETRY_DELAY_USEC,
> > + PSP_I2C_REQ_RETRY_CNT * PSP_I2C_REQ_RETRY_DELAY_USEC,
> > + 0, req);
> > + if (ret)
> > + goto cleanup;
>
> > + if (status) {
> > + ret = status;
> > + goto cleanup;
> > + }
>
> I would write it in this form:
>
> ret = status;
> if (ret)
> goto cleanup;
ACK.
> > + dev_dbg(psp_i2c_dev, "Request accepted by PSP after %ums\n",
> > + jiffies_to_msecs(jiffies - start));
> > +
> > +cleanup:
> > + kfree(req);
> > + return ret;
> > +}
> > +
> > +static int psp_acquire_i2c_bus(void)
> > +{
> > + int status;
> > +
> > + mutex_lock(&psp_i2c_access_mutex);
> > +
> > + /* Return early if mailbox malfunctioned */
> > + if (psp_i2c_mbox_fail)
> > + goto cleanup;
> > +
> > + /*
> > + * Simply increment usage counter and return if PSP semaphore was
> > + * already taken by kernel.
> > + */
> > + if (psp_i2c_access_count > 0) {
>
> ' > 0' is redundant. It's unsigned.
ACK.
>
> > + psp_i2c_access_count++;
> > + goto cleanup;
> > + };
> > +
> > + status = psp_send_i2c_req(PSP_I2C_REQ_ACQUIRE);
> > + if (status) {
> > + if (status == -ETIMEDOUT)
> > + dev_err(psp_i2c_dev, "Timed out waiting for PSP to release I2C bus\n");
> > + else
> > + dev_err(psp_i2c_dev, "PSP communication error\n");
> > +
> > + dev_err(psp_i2c_dev, "Assume i2c bus is for exclusive host usage\n");
> > + psp_i2c_mbox_fail = true;
> > + goto cleanup;
> > + }
> > +
> > + psp_i2c_sem_acquired = jiffies;
> > + psp_i2c_access_count++;
> > +
> > + /*
> > + * In case of errors with PSP arbitrator psp_i2c_mbox_fail variable is
> > + * set above. As a consequence consecutive calls to acquire will bypass
> > + * communication with PSP. At any case i2c bus is granted to the caller,
> > + * thus always return success.
> > + */
> > +cleanup:
> > + mutex_unlock(&psp_i2c_access_mutex);
> > + return 0;
> > +}
> > +
> > +static void psp_release_i2c_bus(void)
> > +{
> > + int status;
> > +
> > + mutex_lock(&psp_i2c_access_mutex);
> > +
> > + /* Return early if mailbox was malfunctional */
> > + if (psp_i2c_mbox_fail)
> > + goto cleanup;
> > +
> > + /*
> > + * If we are last owner of PSP semaphore, need to release aribtration
> > + * via mailbox.
> > + */
> > + psp_i2c_access_count--;
>
> > + if (psp_i2c_access_count > 0)
>
> Ditto.
ACK.
Best Regards,
Jan
