mmc: mvsdio: Use sg_miter for PIO

Use the scatterlist memory iterator instead of just
dereferencing virtual memory using sg_virt().
This make highmem references work properly.

This driver also has a bug in the PIO sglist handling that
is fixed as part of the patch: it does not travers the
list of scatterbuffers: it will just process the first
item in the list. This is fixed by augmenting the logic
such that we do not process more than one sgitem
per IRQ instead of counting down potentially the whole
length of the request.

We can suspect that the PIO path is quite untested.

Suggested-by: Christoph Hellwig <[e-mail]>
Link: https://lore.kernel.org/linux-mmc/[e-mail]/
Signed-off-by: Linus Walleij <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/mmc/host/mvsdio.c

···
 	unsigned int xfer_mode;
 	unsigned int intr_en;
 	unsigned int ctrl;
+	bool use_pio;
+	struct sg_mapping_iter sg_miter;
 	unsigned int pio_size;
-	void *pio_ptr;
 	unsigned int sg_frags;
 	unsigned int ns_per_clk;
 	unsigned int clock;
···
 		 * data when the buffer is not aligned on a 64 byte
 		 * boundary.
 		 */
+		unsigned int miter_flags = SG_MITER_ATOMIC; /* Used from IRQ */
+
+		if (data->flags & MMC_DATA_READ)
+			miter_flags |= SG_MITER_TO_SG;
+		else
+			miter_flags |= SG_MITER_FROM_SG;
+
 		host->pio_size = data->blocks * data->blksz;
-		host->pio_ptr = sg_virt(data->sg);
+		sg_miter_start(&host->sg_miter, data->sg, data->sg_len, miter_flags);
 		if (!nodma)
-			dev_dbg(host->dev, "fallback to PIO for data at 0x%p size %d\n",
-				host->pio_ptr, host->pio_size);
+			dev_dbg(host->dev, "fallback to PIO for data\n");
+		host->use_pio = true;
 		return 1;
 	} else {
 		dma_addr_t phys_addr;
···
 		phys_addr = sg_dma_address(data->sg);
 		mvsd_write(MVSD_SYS_ADDR_LOW, (u32)phys_addr & 0xffff);
 		mvsd_write(MVSD_SYS_ADDR_HI,  (u32)phys_addr >> 16);
+		host->use_pio = false;
 		return 0;
 	}
 }
···
 {
 	void __iomem *iobase = host->base;
 
-	if (host->pio_ptr) {
-		host->pio_ptr = NULL;
+	if (host->use_pio) {
+		sg_miter_stop(&host->sg_miter);
 		host->pio_size = 0;
 	} else {
 		dma_unmap_sg(mmc_dev(host->mmc), data->sg, host->sg_frags,
···
 static irqreturn_t mvsd_irq(int irq, void *dev)
 {
 	struct mvsd_host *host = dev;
+	struct sg_mapping_iter *sgm = &host->sg_miter;
 	void __iomem *iobase = host->base;
 	u32 intr_status, intr_done_mask;
 	int irq_handled = 0;
+	u16 *p;
+	int s;
 
 	intr_status = mvsd_read(MVSD_NOR_INTR_STATUS);
 	dev_dbg(host->dev, "intr 0x%04x intr_en 0x%04x hw_state 0x%04x\n",
···
 	spin_lock(&host->lock);
 
 	/* PIO handling, if needed. Messy business... */
-	if (host->pio_size &&
+	if (host->use_pio) {
+		/*
+		 * As we set sgm->consumed this always gives a valid buffer
+		 * position.
+		 */
+		if (!sg_miter_next(sgm)) {
+			/* This should not happen */
+			dev_err(host->dev, "ran out of scatter segments\n");
+			spin_unlock(&host->lock);
+			host->intr_en &=
+				~(MVSD_NOR_RX_READY | MVSD_NOR_RX_FIFO_8W |
+				  MVSD_NOR_TX_AVAIL | MVSD_NOR_TX_FIFO_8W);
+			mvsd_write(MVSD_NOR_INTR_EN, host->intr_en);
+			return IRQ_HANDLED;
+		}
+		p = sgm->addr;
+		s = sgm->length;
+		if (s > host->pio_size)
+			s = host->pio_size;
+	}
+
+	if (host->use_pio &&
 	    (intr_status & host->intr_en &
 	     (MVSD_NOR_RX_READY | MVSD_NOR_RX_FIFO_8W))) {
-		u16 *p = host->pio_ptr;
-		int s = host->pio_size;
+
 		while (s >= 32 && (intr_status & MVSD_NOR_RX_FIFO_8W)) {
 			readsw(iobase + MVSD_FIFO, p, 16);
 			p += 16;
 			s -= 32;
+			sgm->consumed += 32;
 			intr_status = mvsd_read(MVSD_NOR_INTR_STATUS);
 		}
 		/*
···
 				put_unaligned(mvsd_read(MVSD_FIFO), p++);
 				put_unaligned(mvsd_read(MVSD_FIFO), p++);
 				s -= 4;
+				sgm->consumed += 4;
 				intr_status = mvsd_read(MVSD_NOR_INTR_STATUS);
 			}
 			if (s && s < 4 && (intr_status & MVSD_NOR_RX_READY)) {
···
 				val[0] = mvsd_read(MVSD_FIFO);
 				val[1] = mvsd_read(MVSD_FIFO);
 				memcpy(p, ((void *)&val) + 4 - s, s);
+				sgm->consumed += s;
 				s = 0;
 				intr_status = mvsd_read(MVSD_NOR_INTR_STATUS);
 			}
-			if (s == 0) {
+			/* PIO transfer done */
+			host->pio_size -= sgm->consumed;
+			if (host->pio_size == 0) {
 				host->intr_en &=
 				     ~(MVSD_NOR_RX_READY | MVSD_NOR_RX_FIFO_8W);
 				mvsd_write(MVSD_NOR_INTR_EN, host->intr_en);
···
 		}
 		dev_dbg(host->dev, "pio %d intr 0x%04x hw_state 0x%04x\n",
 			s, intr_status, mvsd_read(MVSD_HW_STATE));
-		host->pio_ptr = p;
-		host->pio_size = s;
 		irq_handled = 1;
-	} else if (host->pio_size &&
+	} else if (host->use_pio &&
 		   (intr_status & host->intr_en &
 		    (MVSD_NOR_TX_AVAIL | MVSD_NOR_TX_FIFO_8W))) {
-		u16 *p = host->pio_ptr;
-		int s = host->pio_size;
 		/*
 		 * The TX_FIFO_8W bit is unreliable. When set, bursting
 		 * 16 halfwords all at once in the FIFO drops data. Actually
···
 			mvsd_write(MVSD_FIFO, get_unaligned(p++));
 			mvsd_write(MVSD_FIFO, get_unaligned(p++));
 			s -= 4;
+			sgm->consumed += 4;
 			intr_status = mvsd_read(MVSD_NOR_INTR_STATUS);
 		}
 		if (s < 4) {
···
 				memcpy(((void *)&val) + 4 - s, p, s);
 				mvsd_write(MVSD_FIFO, val[0]);
 				mvsd_write(MVSD_FIFO, val[1]);
+				sgm->consumed += s;
 				s = 0;
 				intr_status = mvsd_read(MVSD_NOR_INTR_STATUS);
 			}
-			if (s == 0) {
+			/* PIO transfer done */
+			host->pio_size -= sgm->consumed;
+			if (host->pio_size == 0) {
 				host->intr_en &=
 				     ~(MVSD_NOR_TX_AVAIL | MVSD_NOR_TX_FIFO_8W);
 				mvsd_write(MVSD_NOR_INTR_EN, host->intr_en);
···
 		}
 		dev_dbg(host->dev, "pio %d intr 0x%04x hw_state 0x%04x\n",
 			s, intr_status, mvsd_read(MVSD_HW_STATE));
-		host->pio_ptr = p;
-		host->pio_size = s;
 		irq_handled = 1;
 	}