u32 mbr_dus; /* Destination Microblock Stride Register */
};
-
+/* 64-bit alignment needed to update CNDA and CUBC registers in an atomic way. */
struct at_xdmac_desc {
struct at_xdmac_lld lld;
enum dma_transfer_direction direction;
unsigned int xfer_size;
struct list_head descs_list;
struct list_head xfer_node;
-};
+} __aligned(sizeof(u64));
static inline void __iomem *at_xdmac_chan_reg_base(struct at_xdmac *atxdmac, unsigned int chan_nb)
{
* access. Hopefully we can access DDR through both ports (at least on
* SAMA5D4x), so we can use the same interface for source and dest,
* that solves the fact we don't know the direction.
+ * ERRATA: Even if useless for memory transfers, the PERID has to not
+ * match the one of another channel. If not, it could lead to spurious
+ * flag status.
*/
- u32 chan_cc = AT_XDMAC_CC_DIF(0)
+ u32 chan_cc = AT_XDMAC_CC_PERID(0x3f)
+ | AT_XDMAC_CC_DIF(0)
| AT_XDMAC_CC_SIF(0)
| AT_XDMAC_CC_MBSIZE_SIXTEEN
| AT_XDMAC_CC_TYPE_MEM_TRAN;
* access DDR through both ports (at least on SAMA5D4x), so we can use
* the same interface for source and dest, that solves the fact we
* don't know the direction.
+ * ERRATA: Even if useless for memory transfers, the PERID has to not
+ * match the one of another channel. If not, it could lead to spurious
+ * flag status.
*/
- u32 chan_cc = AT_XDMAC_CC_DAM_INCREMENTED_AM
+ u32 chan_cc = AT_XDMAC_CC_PERID(0x3f)
+ | AT_XDMAC_CC_DAM_INCREMENTED_AM
| AT_XDMAC_CC_SAM_INCREMENTED_AM
| AT_XDMAC_CC_DIF(0)
| AT_XDMAC_CC_SIF(0)
* access. Hopefully we can access DDR through both ports (at least on
* SAMA5D4x), so we can use the same interface for source and dest,
* that solves the fact we don't know the direction.
+ * ERRATA: Even if useless for memory transfers, the PERID has to not
+ * match the one of another channel. If not, it could lead to spurious
+ * flag status.
*/
- u32 chan_cc = AT_XDMAC_CC_DAM_UBS_AM
+ u32 chan_cc = AT_XDMAC_CC_PERID(0x3f)
+ | AT_XDMAC_CC_DAM_UBS_AM
| AT_XDMAC_CC_SAM_INCREMENTED_AM
| AT_XDMAC_CC_DIF(0)
| AT_XDMAC_CC_SIF(0)
desc->lld.mbr_cfg = chan_cc;
dev_dbg(chan2dev(chan),
- "%s: lld: mbr_da=%pad, mbr_ds=%pad, mbr_ubc=0x%08x, mbr_cfg=0x%08x\n",
- __func__, &desc->lld.mbr_da, &desc->lld.mbr_ds, desc->lld.mbr_ubc,
+ "%s: lld: mbr_da=%pad, mbr_ds=0x%08x, mbr_ubc=0x%08x, mbr_cfg=0x%08x\n",
+ __func__, &desc->lld.mbr_da, desc->lld.mbr_ds, desc->lld.mbr_ubc,
desc->lld.mbr_cfg);
return desc;
u32 cur_nda, check_nda, cur_ubc, mask, value;
u8 dwidth = 0;
unsigned long flags;
+ bool initd;
ret = dma_cookie_status(chan, cookie, txstate);
if (ret == DMA_COMPLETE)
residue = desc->xfer_size;
/*
* Flush FIFO: only relevant when the transfer is source peripheral
- * synchronized.
+ * synchronized. Flush is needed before reading CUBC because data in
+ * the FIFO are not reported by CUBC. Reporting a residue of the
+ * transfer length while we have data in FIFO can cause issue.
+ * Usecase: atmel USART has a timeout which means I have received
+ * characters but there is no more character received for a while. On
+ * timeout, it requests the residue. If the data are in the DMA FIFO,
+ * we will return a residue of the transfer length. It means no data
+ * received. If an application is waiting for these data, it will hang
+ * since we won't have another USART timeout without receiving new
+ * data.
*/
mask = AT_XDMAC_CC_TYPE | AT_XDMAC_CC_DSYNC;
value = AT_XDMAC_CC_TYPE_PER_TRAN | AT_XDMAC_CC_DSYNC_PER2MEM;
}
/*
- * When processing the residue, we need to read two registers but we
- * can't do it in an atomic way. AT_XDMAC_CNDA is used to find where
- * we stand in the descriptor list and AT_XDMAC_CUBC is used
- * to know how many data are remaining for the current descriptor.
- * Since the dma channel is not paused to not loose data, between the
- * AT_XDMAC_CNDA and AT_XDMAC_CUBC read, we may have change of
- * descriptor.
- * For that reason, after reading AT_XDMAC_CUBC, we check if we are
- * still using the same descriptor by reading a second time
- * AT_XDMAC_CNDA. If AT_XDMAC_CNDA has changed, it means we have to
- * read again AT_XDMAC_CUBC.
+ * The easiest way to compute the residue should be to pause the DMA
+ * but doing this can lead to miss some data as some devices don't
+ * have FIFO.
+ * We need to read several registers because:
+ * - DMA is running therefore a descriptor change is possible while
+ * reading these registers
+ * - When the block transfer is done, the value of the CUBC register
+ * is set to its initial value until the fetch of the next descriptor.
+ * This value will corrupt the residue calculation so we have to skip
+ * it.
+ *
+ * INITD -------- ------------
+ * |____________________|
+ * _______________________ _______________
+ * NDA @desc2 \/ @desc3
+ * _______________________/\_______________
+ * __________ ___________ _______________
+ * CUBC 0 \/ MAX desc1 \/ MAX desc2
+ * __________/\___________/\_______________
+ *
+ * Since descriptors are aligned on 64 bits, we can assume that
+ * the update of NDA and CUBC is atomic.
* Memory barriers are used to ensure the read order of the registers.
- * A max number of retries is set because unlikely it can never ends if
- * we are transferring a lot of data with small buffers.
+ * A max number of retries is set because unlikely it could never ends.
*/
- cur_nda = at_xdmac_chan_read(atchan, AT_XDMAC_CNDA) & 0xfffffffc;
- rmb();
- cur_ubc = at_xdmac_chan_read(atchan, AT_XDMAC_CUBC);
for (retry = 0; retry < AT_XDMAC_RESIDUE_MAX_RETRIES; retry++) {
- rmb();
check_nda = at_xdmac_chan_read(atchan, AT_XDMAC_CNDA) & 0xfffffffc;
-
- if (likely(cur_nda == check_nda))
- break;
-
- cur_nda = check_nda;
+ rmb();
+ initd = !!(at_xdmac_chan_read(atchan, AT_XDMAC_CC) & AT_XDMAC_CC_INITD);
rmb();
cur_ubc = at_xdmac_chan_read(atchan, AT_XDMAC_CUBC);
+ rmb();
+ cur_nda = at_xdmac_chan_read(atchan, AT_XDMAC_CNDA) & 0xfffffffc;
+ rmb();
+
+ if ((check_nda == cur_nda) && initd)
+ break;
}
if (unlikely(retry >= AT_XDMAC_RESIDUE_MAX_RETRIES)) {
goto spin_unlock;
}
+ /*
+ * Flush FIFO: only relevant when the transfer is source peripheral
+ * synchronized. Another flush is needed here because CUBC is updated
+ * when the controller sends the data write command. It can lead to
+ * report data that are not written in the memory or the device. The
+ * FIFO flush ensures that data are really written.
+ */
+ if ((desc->lld.mbr_cfg & mask) == value) {
+ at_xdmac_write(atxdmac, AT_XDMAC_GSWF, atchan->mask);
+ while (!(at_xdmac_chan_read(atchan, AT_XDMAC_CIS) & AT_XDMAC_CIS_FIS))
+ cpu_relax();
+ }
+
/*
* Remove size of all microblocks already transferred and the current
* one. Then add the remaining size to transfer of the current
err_clk_disable:
clk_disable_unprepare(atxdmac->clk);
err_free_irq:
- free_irq(atxdmac->irq, atxdmac->dma.dev);
+ free_irq(atxdmac->irq, atxdmac);
return ret;
}
synchronize_irq(atxdmac->irq);
- free_irq(atxdmac->irq, atxdmac->dma.dev);
+ free_irq(atxdmac->irq, atxdmac);
for (i = 0; i < atxdmac->dma.chancnt; i++) {
struct at_xdmac_chan *atchan = &atxdmac->chan[i];
Code Review / kvmfornfv.git / blobdiff