Date:   Sat, 8 Oct 2022 11:48:42 +0200
From:   Sven Peter <sven@...npeter.dev>
To:     Arminder Singh <arminders208@...look.com>
Cc:     linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, asahi@...ts.linux.dev,
        linuxppc-dev@...ts.ozlabs.org,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Hector Martin <marcan@...can.st>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Nicholas Piggin <npiggin@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v3] i2c/pasemi: PASemi I2C controller IRQ enablement

Hi,

> On 7. Oct 2022, at 02:43, Arminder Singh <arminders208@...look.com> wrote:
> 
> This patch adds IRQ support to the PASemi I2C controller driver to 
> increase the performace of I2C transactions on platforms with PASemi I2C 
> controllers. While primarily intended for Apple silicon platforms, this 
> patch should also help in enabling IRQ support for older PASemi hardware 
> as well should the need arise.
> 
> Signed-off-by: Arminder Singh <arminders208@...look.com>
> ---
> This version of the patch has been tested on an M1 Ultra Mac Studio,
> as well as an M1 MacBook Pro, and userspace launches successfully
> while using the IRQ path for I2C transactions.

I think Wolfram suggested to keep this in the commit message. If in doubt listen to him and not me because he’s much more experienced with the kernel than I am ;)

> 
> This version of the patch only contains fixes to the whitespace and
> alignment issues found in v2 of the patch, and as such the testing that
> Christian Zigotsky did on PASemi hardware for v2 of the patch also applies
> to this version of the patch as well.
> (See v2 patch email thread for the "Tested-by" tag)

You can just collect and keep those tags above your signed off by if you only change things like whitespaces.

> 
> v2 to v3 changes:
> - Fixed some whitespace and alignment issues found in v2 of the patch
> 
> v1 to v2 changes:
> - moved completion setup from pasemi_platform_i2c_probe to
>   pasemi_i2c_common_probe to allow PASemi and Apple platforms to share
>   common completion setup code in case PASemi hardware gets IRQ support
>   added
> - initialized the status variable in pasemi_smb_waitready when going down
>   the non-IRQ path
> - removed an unnecessary cast of dev_id in the IRQ handler
> - fixed alignment of struct member names in i2c-pasemi-core.h
>   (addresses Christophe's feedback in the original submission)
> - IRQs are now disabled after the wait_for_completion_timeout call
>   instead of inside the IRQ handler
>   (prevents the IRQ from going off after the completion times out)
> - changed the request_irq call to a devm_request_irq call to obviate
>   the need for a remove function and a free_irq call
>   (thanks to Sven for pointing this out in the original submission)
> - added a reinit_completion call to pasemi_reset 
>   as a failsafe to prevent missed interrupts from causing the completion
>   to never complete (thanks to Arnd Bergmann for pointing this out)
> - removed the bitmask variable in favor of just using the value
>   directly (it wasn't used anywhere else)
> 
> v2 linked here: https://lore.kernel.org/linux-i2c/MN2PR01MB535821C8058C7814B2F8EEDF9F599@MN2PR01MB5358.prod.exchangelabs.com/
> v1 linked here: https://lore.kernel.org/linux-i2c/MN2PR01MB535838492432C910F2381F929F6F9@MN2PR01MB5358.prod.exchangelabs.com/T/#m11b3504c2667517aad7521514c99ca0e07a9381f
> 
> Hopefully the patch is good to go this time around!
> 
> drivers/i2c/busses/i2c-pasemi-core.c     | 29 ++++++++++++++++++++----
> drivers/i2c/busses/i2c-pasemi-core.h     |  5 ++++
> drivers/i2c/busses/i2c-pasemi-platform.c |  6 +++++
> 3 files changed, 36 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-pasemi-core.c b/drivers/i2c/busses/i2c-pasemi-core.c
> index 9028ffb58cc0..4855144b370e 100644
> --- a/drivers/i2c/busses/i2c-pasemi-core.c
> +++ b/drivers/i2c/busses/i2c-pasemi-core.c
> @@ -21,6 +21,7 @@
> #define REG_MTXFIFO    0x00
> #define REG_MRXFIFO    0x04
> #define REG_SMSTA    0x14
> +#define REG_IMASK    0x18
> #define REG_CTL        0x1c
> #define REG_REV        0x28
> 
> @@ -66,6 +67,7 @@ static void pasemi_reset(struct pasemi_smbus *smbus)
>        val |= CTL_EN;
> 
>    reg_write(smbus, REG_CTL, val);
> +    reinit_completion(&smbus->irq_completion);
> }
> 
> static void pasemi_smb_clear(struct pasemi_smbus *smbus)
> @@ -81,11 +83,18 @@ static int pasemi_smb_waitready(struct pasemi_smbus *smbus)
>    int timeout = 10;
>    unsigned int status;
> 
> -    status = reg_read(smbus, REG_SMSTA);
> -
> -    while (!(status & SMSTA_XEN) && timeout--) {
> -        msleep(1);
> +    if (smbus->use_irq) {
> +        reinit_completion(&smbus->irq_completion);
> +        reg_write(smbus, REG_IMASK, SMSTA_XEN | SMSTA_MTN);
> +        wait_for_completion_timeout(&smbus->irq_completion, msecs_to_jiffies(10));
> +        reg_write(smbus, REG_IMASK, 0);
>        status = reg_read(smbus, REG_SMSTA);
> +    } else {
> +        status = reg_read(smbus, REG_SMSTA);
> +        while (!(status & SMSTA_XEN) && timeout--) {
> +            msleep(1);
> +            status = reg_read(smbus, REG_SMSTA);
> +        }
>    }
> 
>    /* Got NACK? */
> @@ -344,10 +353,14 @@ int pasemi_i2c_common_probe(struct pasemi_smbus *smbus)
> 
>    /* set up the sysfs linkage to our parent device */
>    smbus->adapter.dev.parent = smbus->dev;
> +    smbus->use_irq = 0;
> +    init_completion(&smbus->irq_completion);
> 
>    if (smbus->hw_rev != PASEMI_HW_REV_PCI)
>        smbus->hw_rev = reg_read(smbus, REG_REV);
> 
> +    reg_write(smbus, REG_IMASK, 0);
> +
>    pasemi_reset(smbus);
> 
>    error = devm_i2c_add_adapter(smbus->dev, &smbus->adapter);
> @@ -356,3 +369,11 @@ int pasemi_i2c_common_probe(struct pasemi_smbus *smbus)
> 
>    return 0;
> }
> +
> +irqreturn_t pasemi_irq_handler(int irq, void *dev_id)
> +{
> +    struct pasemi_smbus *smbus = dev_id;
> +
> +    complete(&smbus->irq_completion);

I only realized just now that you also want to disable the interrupt right here by writing to IMASK. This is a level sensitive interrupt at AIC level so the moment this handler returns it will fire again until you reach the write above after the completion wait a bit later.


> +    return IRQ_HANDLED;
> +}
> diff --git a/drivers/i2c/busses/i2c-pasemi-core.h b/drivers/i2c/busses/i2c-pasemi-core.h
> index 4655124a37f3..88821f4e8a9f 100644
> --- a/drivers/i2c/busses/i2c-pasemi-core.h
> +++ b/drivers/i2c/busses/i2c-pasemi-core.h
> @@ -7,6 +7,7 @@
> #include <linux/i2c-smbus.h>
> #include <linux/io.h>
> #include <linux/kernel.h>
> +#include <linux/completion.h>
> 
> #define PASEMI_HW_REV_PCI -1
> 
> @@ -16,6 +17,10 @@ struct pasemi_smbus {
>    void __iomem        *ioaddr;
>    unsigned int         clk_div;
>    int             hw_rev;
> +    int             use_irq;
> +    struct completion     irq_completion;
> };
> 
> int pasemi_i2c_common_probe(struct pasemi_smbus *smbus);
> +
> +irqreturn_t pasemi_irq_handler(int irq, void *dev_id);
> diff --git a/drivers/i2c/busses/i2c-pasemi-platform.c b/drivers/i2c/busses/i2c-pasemi-platform.c
> index 88a54aaf7e3c..e35945a91dbe 100644
> --- a/drivers/i2c/busses/i2c-pasemi-platform.c
> +++ b/drivers/i2c/busses/i2c-pasemi-platform.c
> @@ -49,6 +49,7 @@ static int pasemi_platform_i2c_probe(struct platform_device *pdev)
>    struct pasemi_smbus *smbus;
>    u32 frequency;
>    int error;
> +    int irq_num;
> 
>    data = devm_kzalloc(dev, sizeof(struct pasemi_platform_i2c_data),
>                GFP_KERNEL);
> @@ -82,6 +83,11 @@ static int pasemi_platform_i2c_probe(struct platform_device *pdev)
>    if (error)
>        goto out_clk_disable;
> 
> +    irq_num = platform_get_irq(pdev, 0);
> +    error = devm_request_irq(smbus->dev, irq_num, pasemi_irq_handler, 0, "pasemi_apple_i2c", (void *)smbus);
> +
> +    if (!error)
> +        smbus->use_irq = 1;
>    platform_set_drvdata(pdev, data);
> 
>    return 0;
> -- 
> 2.34.1
> 

Sven 

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