Airoha EN7523 specific bug
--------------------------
We found that some serial console may pull TX line to GROUND during board
boot time. Airoha uses TX line as one of its bootstrap pins. On the EN7523
SoC this may lead to booting in RESERVED boot mode.

It was found that some flashes operates incorrectly in RESERVED mode.
Micron and Skyhigh flashes are definitely affected by the issue,
Winbond flashes are not affected.

Details:
--------
DMA reading of odd pages on affected flashes operates incorrectly. Page
reading offset (start of the page) on hardware level is replaced by 0x10.
Thus results in incorrect data reading. As result OS loading becomes
impossible.

Usage of UBI make things even worse. On attaching, UBI will detects
corruptions (because of wrong reading of odd pages) and will try to
recover. For recovering UBI will erase and write 'damaged' blocks with
a valid information. This will destroy all UBI data.

Non-DMA reading is OK.

This patch detects booting in reserved mode, turn off DMA and print big
fat warning.

Fixes: a403997c12019 ("spi: airoha: add SPI-NAND Flash controller driver")
Signed-off-by: Mikhail Kshevetskiy <mikhail.kshevetskiy@iopsys.eu>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
---
 drivers/spi/spi-airoha-snfi.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-airoha-snfi.c b/drivers/spi/spi-airoha-snfi.c
index 8408aee9c06e..1b91ed07d046 100644
--- a/drivers/spi/spi-airoha-snfi.c
+++ b/drivers/spi/spi-airoha-snfi.c
@@ -1013,6 +1013,11 @@ static const struct spi_controller_mem_ops airoha_snand_mem_ops = {
 	.dirmap_write = airoha_snand_dirmap_write,
 };
 
+static const struct spi_controller_mem_ops airoha_snand_nodma_mem_ops = {
+	.supports_op = airoha_snand_supports_op,
+	.exec_op = airoha_snand_exec_op,
+};
+
 static int airoha_snand_setup(struct spi_device *spi)
 {
 	struct airoha_snand_ctrl *as_ctrl;
@@ -1057,7 +1062,9 @@ static int airoha_snand_probe(struct platform_device *pdev)
 	struct airoha_snand_ctrl *as_ctrl;
 	struct device *dev = &pdev->dev;
 	struct spi_controller *ctrl;
+	bool dma_enable = true;
 	void __iomem *base;
+	u32 sfc_strap;
 	int err;
 
 	ctrl = devm_spi_alloc_host(dev, sizeof(*as_ctrl));
@@ -1092,12 +1099,29 @@ static int airoha_snand_probe(struct platform_device *pdev)
 		return dev_err_probe(dev, PTR_ERR(as_ctrl->spi_clk),
 				     "unable to get spi clk\n");
 
+	if (device_is_compatible(dev, "airoha,en7523-snand")) {
+		err = regmap_read(as_ctrl->regmap_ctrl,
+				  REG_SPI_CTRL_SFC_STRAP, &sfc_strap);
+		if (err)
+			return err;
+
+		if (!(sfc_strap & 0x04)) {
+			dma_enable = false;
+			dev_warn(dev, "Detected booting in RESERVED mode (UART_TXD was short to GND).\n");
+			dev_warn(dev, "This mode is known for incorrect DMA reading of some flashes.\n");
+			dev_warn(dev, "Usage of DMA for flash operations will be disabled to prevent data\n");
+			dev_warn(dev, "damage. Unplug your serial console and power cycle the board\n");
+			dev_warn(dev, "to boot with full performance.\n");
+		}
+	}
+
 	err = dma_set_mask(as_ctrl->dev, DMA_BIT_MASK(32));
 	if (err)
 		return err;
 
 	ctrl->num_chipselect = 2;
-	ctrl->mem_ops = &airoha_snand_mem_ops;
+	ctrl->mem_ops = dma_enable ? &airoha_snand_mem_ops
+				   : &airoha_snand_nodma_mem_ops;
 	ctrl->bits_per_word_mask = SPI_BPW_MASK(8);
 	ctrl->mode_bits = SPI_RX_DUAL;
 	ctrl->setup = airoha_snand_setup;
-- 
2.51.0

On Tue, Nov 25, 2025 at 10:16:33PM +0300, Mikhail Kshevetskiy wrote:

...

> +			dev_warn(dev, "Detected booting in RESERVED mode (UART_TXD was short to GND).\n");
> +			dev_warn(dev, "This mode is known for incorrect DMA reading of some flashes.\n");
> +			dev_warn(dev, "Usage of DMA for flash operations will be disabled to prevent data\n");
> +			dev_warn(dev, "damage. Unplug your serial console and power cycle the board\n");
> +			dev_warn(dev, "to boot with full performance.\n");

One non-critical remark (for the future), the '\n' in the string literals when
we print messages has two meanings:
 - (obviously) new line
 - (seems not so obvious for people) flush the line to the output device

Due to the second property the messages might be interleaved with the other
messages (assuming SMP machine actively doing and printing something), hence
your messages might be split with other and imagine the user who gets in the
middle of the text something like

"Usage of DMA for flash operations will be disabled to prevent data"

The first thought will be "what the heck does this mean?"

TL;DR: place '\n' with a care in the messages to print not only here,
but in general.

-- 
With Best Regards,
Andy Shevchenko

On 11/25/25 23:24, Andy Shevchenko wrote:
> On Tue, Nov 25, 2025 at 10:16:33PM +0300, Mikhail Kshevetskiy wrote:
>
> ...
>
>> +			dev_warn(dev, "Detected booting in RESERVED mode (UART_TXD was short to GND).\n");
>> +			dev_warn(dev, "This mode is known for incorrect DMA reading of some flashes.\n");
>> +			dev_warn(dev, "Usage of DMA for flash operations will be disabled to prevent data\n");
>> +			dev_warn(dev, "damage. Unplug your serial console and power cycle the board\n");
>> +			dev_warn(dev, "to boot with full performance.\n");
> One non-critical remark (for the future), the '\n' in the string literals when
> we print messages has two meanings:
>  - (obviously) new line
>  - (seems not so obvious for people) flush the line to the output device
>
> Due to the second property the messages might be interleaved with the other
> messages (assuming SMP machine actively doing and printing something), hence
> your messages might be split with other and imagine the user who gets in the
> middle of the text something like
>
> "Usage of DMA for flash operations will be disabled to prevent data"
>
> The first thought will be "what the heck does this mean?"
>
> TL;DR: place '\n' with a care in the messages to print not only here,
> but in general.

Thanks for the point. I know this '\n' issue, but you give me an idea
about making it better.

>

On Tue, Nov 25, 2025 at 10:16:33PM +0300, Mikhail Kshevetskiy wrote:
> Airoha EN7523 specific bug
> --------------------------
> We found that some serial console may pull TX line to GROUND during board
> boot time. Airoha uses TX line as one of its bootstrap pins. On the EN7523
> SoC this may lead to booting in RESERVED boot mode.
> 
> It was found that some flashes operates incorrectly in RESERVED mode.
> Micron and Skyhigh flashes are definitely affected by the issue,
> Winbond flashes are not affected.
> 
> Details:
> --------
> DMA reading of odd pages on affected flashes operates incorrectly. Page
> reading offset (start of the page) on hardware level is replaced by 0x10.
> Thus results in incorrect data reading. As result OS loading becomes
> impossible.
> 
> Usage of UBI make things even worse. On attaching, UBI will detects
> corruptions (because of wrong reading of odd pages) and will try to
> recover. For recovering UBI will erase and write 'damaged' blocks with
> a valid information. This will destroy all UBI data.
> 
> Non-DMA reading is OK.
> 
> This patch detects booting in reserved mode, turn off DMA and print big
> fat warning.

LGTM now, thanks!
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>

-- 
With Best Regards,
Andy Shevchenko