• Lv Zheng's avatar
    ACPI: EC: Fix an EC event IRQ storming issue · 1ab69f27
    Lv Zheng authored
    The EC event IRQ (SCI_EVT) can only be handled by submitting QR_EC. As the
    EC driver handles SCI_EVT in a workqueue, after SCI_EVT is flagged and
    before QR_EC is submitted, there is a period risking IRQ storming. EC IRQ
    must be masked for this period but linux EC driver never does so.
    
    No end user notices the IRQ storming and no developer fixes this known
    issue because:
    
     1. The EC IRQ is always edge triggered GPE, and
     2. The kernel can execute no-op EC IRQ handler very fast.
    
    For edge-triggered EC GPE platforms, it is only reported of post-resume EC
    event lost issues, there won't be an IRQ storming. For level triggered EC
    GPE platforms, fortunately the kernel is always fast enough to execute such
    a no-op EC IRQ handler so that the IRQ handler won't be accumulated to
    starve the task contexts, causing a real IRQ storming.
    
    But the IRQ storming actually can still happen when:
    
     1. The EC IRQ performs like level triggered GPE, and
     2. The kernel EC debugging log is turned on but the console is slow enough.
    
    There are more and more platforms using EC GPE as wake GPE where the EC GPE
    is likely designed as level triggered. Then when EC debugging log is
    enabled, the EC IRQ handler is no longer a no-op but dumps IRQ status to
    the consoles. If the consoles are slow enough, the EC IRQs can arrive much
    faster than executing the handler. Finally the accumulated EC event IRQ
    handlers starve the task contexts, causing the IRQ storming to occur, and
    the kernel hangs can be observed during boot/resume.
    
    This patch fixes this issue by masking EC IRQ for this period:
    
     1. Begins when there is an SCI_EVT IRQ pending, and
     2. Ends when there is a QR_EC completed (SCI_EVT acknowledged).
    Tested-by: default avatarWang Wendy <wendy.wang@intel.com>
    Tested-by: default avatarFeng Chenzhou <chenzhoux.feng@intel.com>
    Signed-off-by: default avatarLv Zheng <lv.zheng@intel.com>
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    1ab69f27
ec.c 51.8 KB