The HC_CONTROL_PIO_MODE bit was introduced in the HC_CONTROL register
starting from version 1.1. Therefore, checking the HC_CONTROL_PIO_MODE bit
on hardware that adheres to older specification revisions (i.e., versions
earlier than 1.1) is incorrect. To address this, add an additional check
to read the HCI version before attempting to read the HC_CONTROL_PIO_MODE
status.

Signed-off-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
---
 drivers/i3c/master/mipi-i3c-hci/core.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/i3c/master/mipi-i3c-hci/core.c b/drivers/i3c/master/mipi-i3c-hci/core.c
index b02fbd7882f8..d1952a5619d4 100644
--- a/drivers/i3c/master/mipi-i3c-hci/core.c
+++ b/drivers/i3c/master/mipi-i3c-hci/core.c
@@ -33,6 +33,7 @@
 #define reg_clear(r, v)		reg_write(r, reg_read(r) & ~(v))
 
 #define HCI_VERSION			0x00	/* HCI Version (in BCD) */
+#define HCI_VERSION_V1			0x100   /* MIPI HCI Version number v1.0 */
 
 #define HC_CONTROL			0x04
 #define HC_CONTROL_BUS_ENABLE		BIT(31)
@@ -756,7 +757,7 @@ static int i3c_hci_init(struct i3c_hci *hci)
 	/* Try activating DMA operations first */
 	if (hci->RHS_regs) {
 		reg_clear(HC_CONTROL, HC_CONTROL_PIO_MODE);
-		if (reg_read(HC_CONTROL) & HC_CONTROL_PIO_MODE) {
+		if (regval > HCI_VERSION_V1 && (reg_read(HC_CONTROL) & HC_CONTROL_PIO_MODE)) {
 			dev_err(&hci->master.dev, "PIO mode is stuck\n");
 			ret = -EIO;
 		} else {
@@ -768,7 +769,7 @@ static int i3c_hci_init(struct i3c_hci *hci)
 	/* If no DMA, try PIO */
 	if (!hci->io && hci->PIO_regs) {
 		reg_set(HC_CONTROL, HC_CONTROL_PIO_MODE);
-		if (!(reg_read(HC_CONTROL) & HC_CONTROL_PIO_MODE)) {
+		if (regval > HCI_VERSION_V1 && !(reg_read(HC_CONTROL) & HC_CONTROL_PIO_MODE)) {
 			dev_err(&hci->master.dev, "DMA mode is stuck\n");
 			ret = -EIO;
 		} else {
-- 
2.25.1

Hi

On 8/21/24 4:35 PM, Shyam Sundar S K wrote:
> The HC_CONTROL_PIO_MODE bit was introduced in the HC_CONTROL register
> starting from version 1.1. Therefore, checking the HC_CONTROL_PIO_MODE bit
> on hardware that adheres to older specification revisions (i.e., versions
> earlier than 1.1) is incorrect. To address this, add an additional check
> to read the HCI version before attempting to read the HC_CONTROL_PIO_MODE
> status.
> 
> Signed-off-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
> ---
>   drivers/i3c/master/mipi-i3c-hci/core.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i3c/master/mipi-i3c-hci/core.c b/drivers/i3c/master/mipi-i3c-hci/core.c
> index b02fbd7882f8..d1952a5619d4 100644
> --- a/drivers/i3c/master/mipi-i3c-hci/core.c
> +++ b/drivers/i3c/master/mipi-i3c-hci/core.c
> @@ -33,6 +33,7 @@
>   #define reg_clear(r, v)		reg_write(r, reg_read(r) & ~(v))
>   
>   #define HCI_VERSION			0x00	/* HCI Version (in BCD) */
> +#define HCI_VERSION_V1			0x100   /* MIPI HCI Version number v1.0 */
>   
>   #define HC_CONTROL			0x04
>   #define HC_CONTROL_BUS_ENABLE		BIT(31)
> @@ -756,7 +757,7 @@ static int i3c_hci_init(struct i3c_hci *hci)
>   	/* Try activating DMA operations first */
>   	if (hci->RHS_regs) {
>   		reg_clear(HC_CONTROL, HC_CONTROL_PIO_MODE);
> -		if (reg_read(HC_CONTROL) & HC_CONTROL_PIO_MODE) {
> +		if (regval > HCI_VERSION_V1 && (reg_read(HC_CONTROL) & HC_CONTROL_PIO_MODE)) {
>   			dev_err(&hci->master.dev, "PIO mode is stuck\n");
>   			ret = -EIO;
>   		} else {

Actually here after this patch regval doesn't contain the version but 
HC_CONTROL which is read some line above. HCI_VERSION read is added by 
the patch 3/6 so this patch alone may cause a regression.

I'd say better to use already set hci->version_major and 
hci->version_minor since then code is not vulnerable if some other 
regval = reg_read(OTHER_REG) is added later before this code block.