[v3] tpm_tis_spi: Release chip select when flow control fails

Commit Message

Peijie Shao May 23, 2023, 2:45 a.m. UTC

From: Peijie Shao <[e-mail]>

The failure paths in tpm_tis_spi_transfer() do not deactivate
chip select. Send an empty message (cs_select == 0) to overcome
this.

The patch is tested by two ways.
One way needs to touch hardware:
   1. force pull MISO pin down to GND, it emulates a forever
      'WAIT' timing.
   2. probe cs pin by an oscilloscope.
   3. load tpm_tis_spi.ko.
After loading, dmesg prints:
    "probe of spi0.0 failed with error -110"
and oscilloscope shows cs pin goes high(deactivated) after
the failure. Before the patch, cs pin keeps low.

Second way is by writing a fake spi controller.
   1. implement .transfer_one method, fill all rx buf with 0.
   2. implement .set_cs method, print the state of cs pin.
   we can see cs goes high after the failure.

Signed-off-by: Peijie Shao <[e-mail]>
---
Changes since v1:
    Thanks to BR, Jarkko's suggestions.
    1. Deactivate cs all of the failure path, not only flow control.
    2. change and update comments.
---
Changes since v2:
    Thanks to Paul?Menzel's suggestions.
    1. common commit tag and correct spelling mistakes.
    2. add test steps.
---
 drivers/char/tpm/tpm_tis_spi_main.c | 8 ++++++++
 1 file changed, 8 insertions(+)

Comments

Jarkko Sakkinen May 24, 2023, 2:06 a.m. UTC | #1

On Tue May 23, 2023 at 5:45 AM EEST,  wrote:
> From: Peijie Shao <[e-mail]>
>
> The failure paths in tpm_tis_spi_transfer() do not deactivate
> chip select. Send an empty message (cs_select == 0) to overcome
> this.
>
> The patch is tested by two ways.
> One way needs to touch hardware:
>    1. force pull MISO pin down to GND, it emulates a forever
>       'WAIT' timing.
>    2. probe cs pin by an oscilloscope.
>    3. load tpm_tis_spi.ko.
> After loading, dmesg prints:
>     "probe of spi0.0 failed with error -110"
> and oscilloscope shows cs pin goes high(deactivated) after
> the failure. Before the patch, cs pin keeps low.
>
> Second way is by writing a fake spi controller.
>    1. implement .transfer_one method, fill all rx buf with 0.
>    2. implement .set_cs method, print the state of cs pin.
>    we can see cs goes high after the failure.
>
> Signed-off-by: Peijie Shao <[e-mail]>

Looks good to me + great explanation, thank you.

Reviewed-by: Jarkko Sakkinen <[e-mail]>

BR, Jarkko

Jarkko Sakkinen May 24, 2023, 3:14 a.m. UTC | #2

On Tue May 23, 2023 at 5:45 AM EEST,  wrote:
> From: Peijie Shao <[e-mail]>
>
> The failure paths in tpm_tis_spi_transfer() do not deactivate
> chip select. Send an empty message (cs_select == 0) to overcome
> this.
>
> The patch is tested by two ways.
> One way needs to touch hardware:
>    1. force pull MISO pin down to GND, it emulates a forever
>       'WAIT' timing.
>    2. probe cs pin by an oscilloscope.
>    3. load tpm_tis_spi.ko.
> After loading, dmesg prints:
>     "probe of spi0.0 failed with error -110"
> and oscilloscope shows cs pin goes high(deactivated) after
> the failure. Before the patch, cs pin keeps low.
>
> Second way is by writing a fake spi controller.
>    1. implement .transfer_one method, fill all rx buf with 0.
>    2. implement .set_cs method, print the state of cs pin.
>    we can see cs goes high after the failure.
>
> Signed-off-by: Peijie Shao <[e-mail]>

Thanks I substitute the patch that I applied with this.

Again:

Reviewed-by: Jarkko Sakkinen <[e-mail]>

BR, Jarkko

Patch

diff --git a/drivers/char/tpm/tpm_tis_spi_main.c b/drivers/char/tpm/tpm_tis_spi_main.c
index 1f5207974..9bfaba092 100644
--- a/drivers/char/tpm/tpm_tis_spi_main.c
+++ b/drivers/char/tpm/tpm_tis_spi_main.c
@@ -136,6 +136,14 @@  int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
 	}
 
 exit:
+	if (ret < 0) {
+		/* Deactivate chip select */
+		memset(&spi_xfer, 0, sizeof(spi_xfer));
+		spi_message_init(&m);
+		spi_message_add_tail(&spi_xfer, &m);
+		spi_sync_locked(phy->spi_device, &m);
+	}
+
 	spi_bus_unlock(phy->spi_device->master);
 	return ret;
 }