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SubjectRe: [PATCH] dmaengine: at_xdmac: Fix wrongfull report of a channel as in use
Date
On 20.01.2019 13:04, Vinod Koul wrote:
> Hi Codrin,
>
> On 17-01-19, 16:10, Codrin.Ciubotariu@microchip.com wrote:
>> From: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
>>
>> atchan->status is used for two things:
>> - pass channel interrupts status from interrupt handler to tasklet;
>> - channel information like whether it is cyclic or paused;
>>
>> Since these operations have nothing in common, this patch adds a
>> different struct member to keep the interrupts status.
>>
>> Fixes a bug in which a channel is wrongfully reported as in use when
>> trying to obtain a new descriptior for a previously used cyclic channel.
>
> This looks reasonable but am unable to see how the bug is fixed. Perhaps
> would be great to split the bug part (which can go to fixes) and remove
> the reuse of variable as a subsequent patch..

Hi Vinod,

This patch is the fix, since it moves the operations on atchan->status,
in which the interrupt status register is saved, to a different member
(irq_status). The AT_XDMAC_CHAN_IS_CYCLIC and AT_XDMAC_CHAN_IS_PAUSED
bits have nothing in common with the interrupt status register.

The bug reproduces when a device_terminate_all() is called,
(AT_XDMAC_CHAN_IS_CYCLIC cleared on atchan->status) and then a late End
of Block interrupt arrives (AT_XDMAC_CIS_BIS), which sets bit 0 of
atchan->status. Bit 0 is also used for AT_XDMAC_CHAN_IS_CYCLIC, so when
a new descriptor for a cyclic transfer is created, the driver reports
the channel as in use:

if (test_and_set_bit(AT_XDMAC_CHAN_IS_CYCLIC, &atchan->status)) {
dev_err(chan2dev(chan), "channel currently used\n");
return NULL;
}

I can send v2 if you consider the commit message misleading.

Best regards,
Codrin

>
>>
>> Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
>> ---
>> drivers/dma/at_xdmac.c | 19 ++++++++++---------
>> 1 file changed, 10 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
>> index 4e557684f792..fe69dccfa0c0 100644
>> --- a/drivers/dma/at_xdmac.c
>> +++ b/drivers/dma/at_xdmac.c
>> @@ -203,6 +203,7 @@ struct at_xdmac_chan {
>> u32 save_cim;
>> u32 save_cnda;
>> u32 save_cndc;
>> + u32 irq_status;
>> unsigned long status;
>> struct tasklet_struct tasklet;
>> struct dma_slave_config sconfig;
>> @@ -1580,8 +1581,8 @@ static void at_xdmac_tasklet(unsigned long data)
>> struct at_xdmac_desc *desc;
>> u32 error_mask;
>>
>> - dev_dbg(chan2dev(&atchan->chan), "%s: status=0x%08lx\n",
>> - __func__, atchan->status);
>> + dev_dbg(chan2dev(&atchan->chan), "%s: status=0x%08x\n",
>> + __func__, atchan->irq_status);
>>
>> error_mask = AT_XDMAC_CIS_RBEIS
>> | AT_XDMAC_CIS_WBEIS
>> @@ -1589,15 +1590,15 @@ static void at_xdmac_tasklet(unsigned long data)
>>
>> if (at_xdmac_chan_is_cyclic(atchan)) {
>> at_xdmac_handle_cyclic(atchan);
>> - } else if ((atchan->status & AT_XDMAC_CIS_LIS)
>> - || (atchan->status & error_mask)) {
>> + } else if ((atchan->irq_status & AT_XDMAC_CIS_LIS)
>> + || (atchan->irq_status & error_mask)) {
>> struct dma_async_tx_descriptor *txd;
>>
>> - if (atchan->status & AT_XDMAC_CIS_RBEIS)
>> + if (atchan->irq_status & AT_XDMAC_CIS_RBEIS)
>> dev_err(chan2dev(&atchan->chan), "read bus error!!!");
>> - if (atchan->status & AT_XDMAC_CIS_WBEIS)
>> + if (atchan->irq_status & AT_XDMAC_CIS_WBEIS)
>> dev_err(chan2dev(&atchan->chan), "write bus error!!!");
>> - if (atchan->status & AT_XDMAC_CIS_ROIS)
>> + if (atchan->irq_status & AT_XDMAC_CIS_ROIS)
>> dev_err(chan2dev(&atchan->chan), "request overflow error!!!");
>>
>> spin_lock(&atchan->lock);
>> @@ -1652,7 +1653,7 @@ static irqreturn_t at_xdmac_interrupt(int irq, void *dev_id)
>> atchan = &atxdmac->chan[i];
>> chan_imr = at_xdmac_chan_read(atchan, AT_XDMAC_CIM);
>> chan_status = at_xdmac_chan_read(atchan, AT_XDMAC_CIS);
>> - atchan->status = chan_status & chan_imr;
>> + atchan->irq_status = chan_status & chan_imr;
>> dev_vdbg(atxdmac->dma.dev,
>> "%s: chan%d: imr=0x%x, status=0x%x\n",
>> __func__, i, chan_imr, chan_status);
>> @@ -1666,7 +1667,7 @@ static irqreturn_t at_xdmac_interrupt(int irq, void *dev_id)
>> at_xdmac_chan_read(atchan, AT_XDMAC_CDA),
>> at_xdmac_chan_read(atchan, AT_XDMAC_CUBC));
>>
>> - if (atchan->status & (AT_XDMAC_CIS_RBEIS | AT_XDMAC_CIS_WBEIS))
>> + if (atchan->irq_status & (AT_XDMAC_CIS_RBEIS | AT_XDMAC_CIS_WBEIS))
>> at_xdmac_write(atxdmac, AT_XDMAC_GD, atchan->mask);
>>
>> tasklet_schedule(&atchan->tasklet);
>> --
>> 2.17.1
>

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