Re: [PATCH arm/aspeed/ast2500 v2] ipmi: add an Aspeed KCS IPMI BMC driver

["Wang, Haiyue" <haiyue.wang@linux.intel.com>]

On 2018-01-25 01:48, Corey Minyard wrote:
> On 01/24/2018 10:06 AM, Haiyue Wang wrote:
>> The KCS (Keyboard Controller Style) interface is used to perform in-band
>> IPMI communication between a server host and its BMC (BaseBoard 
>> Management
>> Controllers).
>>
>> This driver exposes the KCS interface on ASpeed SOCs (AST2400 and 
>> AST2500)
>> as a character device. Such SOCs are commonly used as BMCs and this 
>> driver
>> implements the BMC side of the KCS interface.
>>
>> Signed-off-by: Haiyue Wang <haiyue.wang@linux.intel.com>
>>
>> ---
>> v1->v2
>>
>> - Divide the driver into two parts, one handles the BMC KCS IPMI 2.0 
>> state;
>>    the other handles the BMC KCS controller such as AST2500 IO 
>> accessing.
>> - Use the spin lock APIs to handle the device file operations and BMC 
>> chip
>>    IRQ inferface for accessing the same KCS BMC data structure.
>> - Enhanced the phases handling of the KCS BMC.
>> - Unified the IOCTL definition for IPMI BMC, it will be used by KCS 
>> and BT.
>>
>> ---
>>
>> +
>> +static void kcs_bmc_handle_data(struct kcs_bmc *kcs_bmc)
>> +{
>> +    u8 data;
>> +
>> +    switch (kcs_bmc->phase) {
>> +    case KCS_PHASE_WRITE:
>> +        set_state(kcs_bmc, WRITE_STATE);
>> +
>> +        /* set OBF before reading data */
>> +        write_data(kcs_bmc, KCS_ZERO_DATA);
>> +
>> +        if (kcs_bmc->data_in_idx < KCS_MSG_BUFSIZ)
>> +            kcs_bmc->data_in[kcs_bmc->data_in_idx++] =
>> +                        read_data(kcs_bmc);
>> +        break;
>> +
>> +    case KCS_PHASE_WRITE_END:
>> +        set_state(kcs_bmc, READ_STATE);
>> +
>> +        if (kcs_bmc->data_in_idx < KCS_MSG_BUFSIZ)
>> +            kcs_bmc->data_in[kcs_bmc->data_in_idx++] =
>> +                        read_data(kcs_bmc);
>> +
>> +        kcs_bmc->phase = KCS_PHASE_WAIT_READ;
>> +        if (kcs_bmc->running) {
>
> Why do you only do this when running is set?  It won't hurt anything 
> if it's not
> set.  As it is, you have a race if something opens the device while 
> this code
> runs.
>
> Also, don't set the state to wait read until the "write" has finished 
> (userland has
> read the data out of the buffer.  More on that later.
>
Understood.
>> +            kcs_bmc->data_in_avail = true;
>> +            wake_up_interruptible(&kcs_bmc->queue);
>> +        }
>> +        break;
>> +
>> +    case KCS_PHASE_READ:
>> +        if (kcs_bmc->data_out_idx == kcs_bmc->data_out_len)
>> +            set_state(kcs_bmc, IDLE_STATE);
>> +
>> +        data = read_data(kcs_bmc);
>> +        if (data != KCS_CMD_READ_BYTE) {
>> +            set_state(kcs_bmc, ERROR_STATE);
>> +            write_data(kcs_bmc, KCS_ZERO_DATA);
>> +            break;
>> +        }
>> +
>> +        if (kcs_bmc->data_out_idx == kcs_bmc->data_out_len) {
>> +            write_data(kcs_bmc, KCS_ZERO_DATA);
>> +            kcs_bmc->phase = KCS_PHASE_IDLE;
>> +            break;
>> +        }
>> +
>> +        write_data(kcs_bmc,
>> +            kcs_bmc->data_out[kcs_bmc->data_out_idx++]);
>> +        break;
>> +
>> +    case KCS_PHASE_ABORT_ERROR1:
>> +        set_state(kcs_bmc, READ_STATE);
>> +
>> +        /* Read the Dummy byte */
>> +        read_data(kcs_bmc);
>> +
>> +        write_data(kcs_bmc, kcs_bmc->error);
>> +        kcs_bmc->phase = KCS_PHASE_ABORT_ERROR2;
>> +        break;
>> +
>> +    case KCS_PHASE_ABORT_ERROR2:
>> +        set_state(kcs_bmc, IDLE_STATE);
>> +
>> +        /* Read the Dummy byte */
>> +        read_data(kcs_bmc);
>> +
>> +        write_data(kcs_bmc, KCS_ZERO_DATA);
>> +        kcs_bmc->phase = KCS_PHASE_IDLE;
>> +
>> +        break;
>> +
>> +    default:
>> +        set_state(kcs_bmc, ERROR_STATE);
>> +
>> +        /* Read the Dummy byte */
>> +        read_data(kcs_bmc);
>> +
>> +        write_data(kcs_bmc, KCS_ZERO_DATA);
>> +        break;
>> +    }
>> +}
>> +
>> +static void kcs_bmc_handle_command(struct kcs_bmc *kcs_bmc)
>> +{
>> +    u8 cmd;
>> +
>> +    set_state(kcs_bmc, WRITE_STATE);
>> +
>> +    /* Dummy data to generate OBF */
>> +    write_data(kcs_bmc, KCS_ZERO_DATA);
>> +
>> +    cmd = read_data(kcs_bmc);
>
> Shouldn't you check the phase in all the cases below and do error
> handling if the phase isn't correct?
>
> Similar thing if the device here isn't open.  You need to handle
> that gracefully.
>
> Also, you should remove data_in_avail and data_in_idx setting from
> here, for reasons I will explain later.
>
If host software sends the data twice such as a retry before the BMC's 
IPMI service starts,
then the two IPMI requests will be merged into one, if not clear 
data_in_idx after receving
KCS_CMD_WRITE_START. Most of the states are driven by host software 
(SMS). :(
>> +    switch (cmd) {
>> +    case KCS_CMD_WRITE_START:
>> +        kcs_bmc->data_in_avail = false;
>> +        kcs_bmc->data_in_idx   = 0;
>> +        kcs_bmc->phase         = KCS_PHASE_WRITE;
>> +        kcs_bmc->error         = KCS_NO_ERROR;
>> +        break;
>> +
>> +    case KCS_CMD_WRITE_END:
>> +        kcs_bmc->phase = KCS_PHASE_WRITE_END;
>> +        break;
>> +
>> +    case KCS_CMD_ABORT:
>> +        if (kcs_bmc->error == KCS_NO_ERROR)
>> +            kcs_bmc->error = KCS_ABORTED_BY_COMMAND;
>> +
>> +        kcs_bmc->phase = KCS_PHASE_ABORT_ERROR1;
>> +        break;
>> +
>> +    default:
>> +        kcs_bmc->error = KCS_ILLEGAL_CONTROL_CODE;
>> +        set_state(kcs_bmc, ERROR_STATE);
>> +        write_data(kcs_bmc, kcs_bmc->error);
>> +        kcs_bmc->phase = KCS_PHASE_ERROR;
>> +        break;
>> +    }
>> +}
>> +
>> +int kcs_bmc_handle_event(struct kcs_bmc *kcs_bmc)
>> +{
>> +    unsigned long flags;
>> +    int ret = 0;
>> +    u8 status;
>> +
>> +    spin_lock_irqsave(&kcs_bmc->lock, flags);
>> +
>> +    status = read_status(kcs_bmc) & (KCS_STATUS_IBF | 
>> KCS_STATUS_CMD_DAT);
>> +
>> +    switch (status) {
>> +    case KCS_STATUS_IBF | KCS_STATUS_CMD_DAT:
>> +        kcs_bmc_handle_command(kcs_bmc);
>> +        break;
>> +
>> +    case KCS_STATUS_IBF:
>> +        kcs_bmc_handle_data(kcs_bmc);
>> +        break;
>> +
>> +    default:
>> +        ret = -1;
>> +        break;
>> +    }
>> +
>> +    spin_unlock_irqrestore(&kcs_bmc->lock, flags);
>> +
>> +    return ret;
>> +}
>> +EXPORT_SYMBOL(kcs_bmc_handle_event);
>> +
>> +static inline struct kcs_bmc *file_kcs_bmc(struct file *filp)
>> +{
>> +    return container_of(filp->private_data, struct kcs_bmc, miscdev);
>> +}
>> +
>> +static int kcs_bmc_open(struct inode *inode, struct file *filp)
>> +{
>> +    struct kcs_bmc *kcs_bmc = file_kcs_bmc(filp);
>> +    int ret = 0;
>> +
>> +    spin_lock_irq(&kcs_bmc->lock);
>> +
>> +    if (!kcs_bmc->running) {
>> +        kcs_bmc->running       = 1;
>> +        kcs_bmc->phase         = KCS_PHASE_IDLE;
>> +        kcs_bmc->data_in_avail = false;
>
> If you do everything right, setting the phase and data_in_avail should 
> not
> be necessary here.
>
>> +    } else {
>> +        ret = -EBUSY;
>> +    }
>> +
>> +    spin_unlock_irq(&kcs_bmc->lock);
>> +
>> +    return ret;
>> +}
>> +
>> +static unsigned int kcs_bmc_poll(struct file *filp, poll_table *wait)
>> +{
>> +    struct kcs_bmc *kcs_bmc = file_kcs_bmc(filp);
>> +    unsigned int mask = 0;
>> +
>> +    poll_wait(filp, &kcs_bmc->queue, wait);
>> +
>> +    spin_lock_irq(&kcs_bmc->lock);
>> +
>> +    if (kcs_bmc->data_in_avail)
>> +        mask |= POLLIN;
>> +
>> +    spin_unlock_irq(&kcs_bmc->lock);
>> +
>> +    return mask;
>> +}
>> +
>> +static ssize_t kcs_bmc_read(struct file *filp, char *buf,
>> +                size_t count, loff_t *offset)
>> +{
>> +    struct kcs_bmc *kcs_bmc = file_kcs_bmc(filp);
>> +    ssize_t ret = -EAGAIN;
>> +
>
> This function still has some issues.
>
> You can't call copy_to_user() with a spinlock held or interrupts 
> disabled.
> To handle readers, you probably need a separate mutex.
>
> Also, this function can return -EAGAIN even if O_NONBLOCK is not set if
> kcs_bmc->data_in_avail changes between when you wait on the event
> and when you check it under the lock.
>
> You also clear data_in_avail even if the copy_to_user() fails, which is
> wrong.
>
> I believe the best way to handle this would be to have the spinlock
> protect the inner workings of the state machine and a mutex handle
> copying data out, setting/clearing the running flag (thus a mutex
> instead of spinlock in open and release) and the ioctl settings (except
> for abort where you will need to grab the spinlock).
>
> After the wait event below, grab the mutex.  If data is not available
> and O_NONBLOCK is not set, drop the mutex and retry.  Otherwise
> this is the only place (besides release) that sets data_in_avail to 
> false.
> Do the copy_to_user(), grab the spinlock, clear data_in_avail and
> data_in_idx, then release the lock and mutex.  If you are really
> adventurous you can do this without grabbing the lock using
> barriers, but it's probably not necessary here.
>
>> +    if (!(filp->f_flags & O_NONBLOCK))
>> +        wait_event_interruptible(kcs_bmc->queue,
>> +                     kcs_bmc->data_in_avail);
>> +
>> +    spin_lock_irq(&kcs_bmc->lock);
>> +
>> +    if (kcs_bmc->data_in_avail) {
>> +        kcs_bmc->data_in_avail = false;
>> +
>> +        if (count > kcs_bmc->data_in_idx)
>> +            count = kcs_bmc->data_in_idx;
>> +
>> +        if (!copy_to_user(buf, kcs_bmc->data_in, count))
>> +            ret = count;
>> +        else
>> +            ret = -EFAULT;
>> +    }
>> +
>> +    spin_unlock_irq(&kcs_bmc->lock);
>> +
>> +    return ret;
>> +}
>> +
>> +static ssize_t kcs_bmc_write(struct file *filp, const char *buf,
>> +                 size_t count, loff_t *offset)
>> +{
>> +    struct kcs_bmc *kcs_bmc = file_kcs_bmc(filp);
>> +    ssize_t ret = count;
>> +
>> +    if (count < 1 || count > KCS_MSG_BUFSIZ)
>> +        return -EINVAL;
>> +
>> +    spin_lock_irq(&kcs_bmc->lock);
>> +
>> +    if (kcs_bmc->phase == KCS_PHASE_WAIT_READ) {
>> +        if (copy_from_user(kcs_bmc->data_out, buf, count)) {
>> +            spin_unlock_irq(&kcs_bmc->lock);
>> +            return -EFAULT;
>> +        }
>> +
>> +        kcs_bmc->phase = KCS_PHASE_READ;
>> +        kcs_bmc->data_out_idx = 1;
>> +        kcs_bmc->data_out_len = count;
>> +        write_data(kcs_bmc, kcs_bmc->data_out[0]);
>> +    } else if (kcs_bmc->phase == KCS_PHASE_READ) {
>> +        ret = -EBUSY;
>> +    } else {
>> +        ret = -EINVAL;
>
> Is there a reason you return -EINVAL here?  Why not just -EBUSY in all
> cases?  Is there something that userland will need to do differently?
>
>> +    }
>> +
>> +    spin_unlock_irq(&kcs_bmc->lock);
>> +
>> +    return ret;
>> +}
>> +
>> +static long kcs_bmc_ioctl(struct file *filp, unsigned int cmd,
>> +              unsigned long arg)
>> +{
>> +    struct kcs_bmc *kcs_bmc = file_kcs_bmc(filp);
>> +    long ret = 0;
>> +
>> +    spin_lock_irq(&kcs_bmc->lock);
>> +
>> +    switch (cmd) {
>> +    case IPMI_BMC_IOCTL_SET_SMS_ATN:
>> +        update_status_bits(kcs_bmc, KCS_STATUS_SMS_ATN,
>> +                        KCS_STATUS_SMS_ATN);
>> +        break;
>> +
>> +    case IPMI_BMC_IOCTL_CLEAR_SMS_ATN:
>> +        update_status_bits(kcs_bmc, KCS_STATUS_SMS_ATN,
>> +                        0);
>> +        break;
>> +
>> +    case IPMI_BMC_IOCTL_FORCE_ABORT:
>> +        set_state(kcs_bmc, ERROR_STATE);
>> +        read_data(kcs_bmc);
>> +        write_data(kcs_bmc, KCS_ZERO_DATA);
>> +
>> +        kcs_bmc->phase = KCS_PHASE_ERROR;
>> +        kcs_bmc->data_in_avail = false;
>> +        break;
>> +
>> +    default:
>> +        ret = -EINVAL;
>> +        break;
>> +    }
>> +
>> +    spin_unlock_irq(&kcs_bmc->lock);
>> +
>> +    return ret;
>> +}
>> +
>> +static int kcs_bmc_release(struct inode *inode, struct file *filp)
>> +{
>> +    struct kcs_bmc *kcs_bmc = file_kcs_bmc(filp);
>> +
>
> What happens if the device gets closed in the middle of a 
> transaction?  That's
> an important case to handle.  If something is in process, you need to 
> abort it.
>
The device just provides the read & write data, the transaction is 
handled in the KCS
controller's IRQ handler.
>> +    spin_lock_irq(&kcs_bmc->lock);
>> +
>> +    kcs_bmc->running = 0;
>> +
>> +    spin_unlock_irq(&kcs_bmc->lock);
>> +
>> +    return 0;
>> +}
>> +