Re: [PATCH v3 4/4] i2c: i2c-qcom-geni: Enable i2c controller sharing between two subsystems

Bjorn Andersson
2024-09-30T03:46:40Z

On Fri, Sep 27, 2024 at 12:01:08PM GMT, Mukesh Kumar Savaliya wrote:
> Add support to share I2C SE by two Subsystems in a mutually exclusive way.
> Use "qcom,shared-se" flag in a particular i2c instance node if the usecase
> requires i2c controller to be shared.
>

Please start your commit message by describing the problem your patch
is solving.

> Sharing of SE(Serial engine) is possible only for GSI mode as each
> subsystem(SS) can queue transfers over its own GPII Channel. For non GSI
> mode, we should force disable this feature even if set by user from DT by
> mistake.
>
> I2C driver just need to mark first_msg and last_msg flag to help indicate
> GPI driver to take lock and unlock TRE there by protecting from concurrent
> access from other EE or Subsystem.
>
> gpi_create_i2c_tre() function at gpi.c will take care of adding Lock and
> Unlock TRE for the respective transfer operations.
>
> Since the GPIOs are also shared between two SS, do not unconfigure them
> during runtime suspend. This will allow other SS to continue to transfer
> the data without any disturbance over the IO lines.
>

This last paragraph describes patch 3, right?

> Signed-off-by: Mukesh Kumar Savaliya <quic_msavaliy@quicinc.com>
> ---
> drivers/i2c/busses/i2c-qcom-geni.c | 24 ++++++++++++++++++++----
> 1 file changed, 20 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-qcom-geni.c b/drivers/i2c/busses/i2c-qcom-geni.c
> index 212336f724a6..479fa8e1c33f 100644
> --- a/drivers/i2c/busses/i2c-qcom-geni.c
> +++ b/drivers/i2c/busses/i2c-qcom-geni.c
> @@ -1,5 +1,6 @@
> // SPDX-License-Identifier: GPL-2.0
> // Copyright (c) 2017-2018, The Linux Foundation. All rights reserved.
> +// Copyright (c) 2024 Qualcomm Innovation Center, Inc. All rights reserved.
>
> #include <linux/acpi.h>
> #include <linux/clk.h>
> @@ -602,6 +603,7 @@ static int geni_i2c_gpi_xfer(struct geni_i2c_dev *gi2c, struct i2c_msg msgs[], i
> peripheral.clk_div = itr->clk_div;
> peripheral.set_config = 1;
> peripheral.multi_msg = false;
> + peripheral.shared_se = gi2c->se.shared_geni_se;
>
> for (i = 0; i < num; i++) {
> gi2c->cur = &msgs[i];
> @@ -612,6 +614,8 @@ static int geni_i2c_gpi_xfer(struct geni_i2c_dev *gi2c, struct i2c_msg msgs[], i
> if (i < num - 1)
> peripheral.stretch = 1;
>
> + peripheral.first_msg = (i == 0);
> + peripheral.last_msg = (i == num - 1);

There are multiple error paths in this loop, which would result in us
never issuing the unlock TRE - effectively blocking other subsystems
from accessing the serial engine until we perform our next access
(assuming that APSS issuing a lock TRE when APSS already has the channel
locked isn't a problem?)

> peripheral.addr = msgs[i].addr;
>
> ret = geni_i2c_gpi(gi2c, &msgs[i], &config,
> @@ -631,8 +635,11 @@ static int geni_i2c_gpi_xfer(struct geni_i2c_dev *gi2c, struct i2c_msg msgs[], i
> dma_async_issue_pending(gi2c->tx_c);
>
> time_left = wait_for_completion_timeout(&gi2c->done, XFER_TIMEOUT);
> - if (!time_left)
> + if (!time_left) {
> + dev_dbg(gi2c->se.dev, "I2C timeout gpi flags:%d addr:0x%x\n",
> + gi2c->cur->flags, gi2c->cur->addr);

This looks useful, but unrelated to this patch.

> gi2c->err = -ETIMEDOUT;
> + }
>
> if (gi2c->err) {
> ret = gi2c->err;
> @@ -800,6 +807,11 @@ static int geni_i2c_probe(struct platform_device *pdev)
> gi2c->clk_freq_out = KHZ(100);
> }
>
> + if (of_property_read_bool(pdev->dev.of_node, "qcom,shared-se")) {
> + gi2c->se.shared_geni_se = true;

gi2c->se.shared_geni_se = of_property_read_bool(dev->of_node, "qcom,shared-se");

> + dev_dbg(&pdev->dev, "I2C is shared between subsystems\n");
> + }
> +
> if (has_acpi_companion(dev))
> ACPI_COMPANION_SET(&gi2c->adap.dev, ACPI_COMPANION(dev));
>
> @@ -870,8 +882,10 @@ static int geni_i2c_probe(struct platform_device *pdev)
> else
> fifo_disable = readl_relaxed(gi2c->se.base + GENI_IF_DISABLE_RO) & FIFO_IF_DISABLE;
>
> - if (fifo_disable) {
> - /* FIFO is disabled, so we can only use GPI DMA */
> + if (fifo_disable || gi2c->se.shared_geni_se) {
> + /* FIFO is disabled, so we can only use GPI DMA.
> + * SE can be shared in GSI mode between subsystems, each SS owns a GPII.
> + **/

I think you're trying to document why we're entering the "GPI-only"
branch. The addition you made was that if the user has requested
"shared-se", then it's GPI-only.

But I'm not able to wrap my head around your addition here. Why does it
matter that each subsystem own a GPII? Is that a reason for choosing
GPI-only mode?

> gi2c->gpi_mode = true;
> ret = setup_gpi_dma(gi2c);
> if (ret) {
> @@ -883,6 +897,9 @@ static int geni_i2c_probe(struct platform_device *pdev)
> dev_dbg(dev, "Using GPI DMA mode for I2C\n");
> } else {
> gi2c->gpi_mode = false;
> +
> + /* Force disable shared SE case for non GSI mode */

GSI or GPI mode?

> + gi2c->se.shared_geni_se = false;

If shared_geni_se was true prior to this assignment, wouldn't we have
entered the if (fifo_disable ...) branch?

> tx_depth = geni_se_get_tx_fifo_depth(&gi2c->se);
>
> /* I2C Master Hub Serial Elements doesn't have the HW_PARAM_0 register */
> @@ -964,7 +981,6 @@ static int __maybe_unused geni_i2c_runtime_suspend(struct device *dev)
> if (ret) {
> enable_irq(gi2c->irq);
> return ret;
> -

Please avoid such unrelated cleanups.

Regards,
Bjorn

> } else {
> gi2c->suspended = 1;
> }
> --
> 2.25.1
>