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    Subject[PATCH v5 4/4] mmc: dw_mmc: Protect read-modify-write of INTMASK with a lock
    Date
    We're running into cases where our enabling of the SDIO interrupt in
    dw_mmc doesn't actually take effect. Specifically, adding patch like
    this:

    +++ b/drivers/mmc/host/dw_mmc.c
    @@ -1076,6 +1076,9 @@ static void dw_mci_enable_sdio_irq(struct mmc_host *mmc, int enb)

    mci_writel(host, INTMASK,
    (int_mask | SDMMC_INT_SDIO(slot->id)));
    + int_mask = mci_readl(host, INTMASK);
    + if (!(int_mask & SDMMC_INT_SDIO(slot->id)))
    + dev_err(&mmc->class_dev, "failed to enable sdio irq\n");
    } else {
    ...actually triggers the error message. That's because the
    dw_mci_enable_sdio_irq() unsafely does a read-modify-write of the
    INTMASK register.

    We can't just use the standard host->lock since that lock is not irq
    safe and mmc_signal_sdio_irq() (called from interrupt context) calls
    dw_mci_enable_sdio_irq(). Add a new irq-safe lock to protect INTMASK.

    An alternate solution to this is to punt mmc_signal_sdio_irq() to the
    tasklet and then protect INTMASK modifications by the standard host
    lock. This seemed like a bit more of a high-latency change.

    Reported-by: Bing Zhao <bzhao@marvell.com>
    Signed-off-by: Doug Anderson <dianders@chromium.org>
    Reviewed-by: James Hogan <james.hogan@imgtec.com>
    ---
    Changes in v5: None
    Changes in v3: None
    Changes in v2:
    - intmask_lock renamed to irq_lock
    drivers/mmc/host/dw_mmc.c | 13 +++++++++++++
    include/linux/mmc/dw_mmc.h | 6 ++++++
    2 files changed, 19 insertions(+)
    diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
    index ae10a02..64ea042 100644
    --- a/drivers/mmc/host/dw_mmc.c
    +++ b/drivers/mmc/host/dw_mmc.c
    @@ -759,6 +759,7 @@ disable:

    static int dw_mci_submit_data_dma(struct dw_mci *host, struct mmc_data *data)
    {
    + unsigned long irqflags;
    int sg_len;
    u32 temp;

    @@ -795,9 +796,11 @@ static int dw_mci_submit_data_dma(struct dw_mci *host, struct mmc_data *data)
    mci_writel(host, CTRL, temp);

    /* Disable RX/TX IRQs, let DMA handle it */
    + spin_lock_irqsave(&host->irq_lock, irqflags);
    temp = mci_readl(host, INTMASK);
    temp &= ~(SDMMC_INT_RXDR | SDMMC_INT_TXDR);
    mci_writel(host, INTMASK, temp);
    + spin_unlock_irqrestore(&host->irq_lock, irqflags);

    host->dma_ops->start(host, sg_len);

    @@ -806,6 +809,7 @@ static int dw_mci_submit_data_dma(struct dw_mci *host, struct mmc_data *data)

    static void dw_mci_submit_data(struct dw_mci *host, struct mmc_data *data)
    {
    + unsigned long irqflags;
    u32 temp;

    data->error = -EINPROGRESS;
    @@ -834,9 +838,12 @@ static void dw_mci_submit_data(struct dw_mci *host, struct mmc_data *data)
    host->part_buf_count = 0;

    mci_writel(host, RINTSTS, SDMMC_INT_TXDR | SDMMC_INT_RXDR);
    +
    + spin_lock_irqsave(&host->irq_lock, irqflags);
    temp = mci_readl(host, INTMASK);
    temp |= SDMMC_INT_TXDR | SDMMC_INT_RXDR;
    mci_writel(host, INTMASK, temp);
    + spin_unlock_irqrestore(&host->irq_lock, irqflags);

    temp = mci_readl(host, CTRL);
    temp &= ~SDMMC_CTRL_DMA_ENABLE;
    @@ -1284,8 +1291,11 @@ static void dw_mci_enable_sdio_irq(struct mmc_host *mmc, int enb)
    {
    struct dw_mci_slot *slot = mmc_priv(mmc);
    struct dw_mci *host = slot->host;
    + unsigned long irqflags;
    u32 int_mask;

    + spin_lock_irqsave(&host->irq_lock, irqflags);
    +
    /* Enable/disable Slot Specific SDIO interrupt */
    int_mask = mci_readl(host, INTMASK);
    if (enb)
    @@ -1293,6 +1303,8 @@ static void dw_mci_enable_sdio_irq(struct mmc_host *mmc, int enb)
    else
    int_mask &= ~SDMMC_INT_SDIO(slot->sdio_id);
    mci_writel(host, INTMASK, int_mask);
    +
    + spin_unlock_irqrestore(&host->irq_lock, irqflags);
    }

    static int dw_mci_execute_tuning(struct mmc_host *mmc, u32 opcode)
    @@ -2661,6 +2673,7 @@ int dw_mci_probe(struct dw_mci *host)
    host->quirks = host->pdata->quirks;

    spin_lock_init(&host->lock);
    + spin_lock_init(&host->irq_lock);
    INIT_LIST_HEAD(&host->queue);

    /*
    diff --git a/include/linux/mmc/dw_mmc.h b/include/linux/mmc/dw_mmc.h
    index 42b724e..471fb31 100644
    --- a/include/linux/mmc/dw_mmc.h
    +++ b/include/linux/mmc/dw_mmc.h
    @@ -106,6 +106,11 @@ struct mmc_data;
    * @cur_slot, @mrq and @state. These must always be updated
    * at the same time while holding @lock.
    *
    + * @irq_lock is an irq-safe spinlock protecting the INTMASK register
    + * to allow the interrupt handler to modify it directly. Held for only long
    + * enough to read-modify-write INTMASK and no other locks are grabbed when
    + * holding this one.
    + *
    * The @mrq field of struct dw_mci_slot is also protected by @lock,
    * and must always be written at the same time as the slot is added to
    * @queue.
    @@ -125,6 +130,7 @@ struct mmc_data;
    */
    struct dw_mci {
    spinlock_t lock;
    + spinlock_t irq_lock;
    void __iomem *regs;

    struct scatterlist *sg;
    --
    2.2.0.rc0.207.ga3a616c


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