linux-kernel - Re: [PATCH] usb: typec: tipd: drop double register read in tps6598x

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Message-ID: <87bjld51h3.fsf@dell.be.48ers.dk>
Date: Fri, 07 Nov 2025 16:03:36 +0100
From: Peter Korsgaard <peter@...sgaard.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: javier.carrasco@...fvision.net,  heikki.krogerus@...ux.intel.com,
  neal@...pa.dev,  linux-usb@...r.kernel.org,  linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: typec: tipd: drop double register read in
 tps6598x_interrupt

>>>>> "Greg" == Greg KH <gregkh@...uxfoundation.org> writes:

 > On Thu, Nov 06, 2025 at 05:48:49PM +0100, Peter Korsgaard wrote:
 >> Commit 409c1cfb5a80 ("usb: typec: tipd: fix event checking for tps6598x")
 >> added (by accident?) a double read of the TPS_REG_INT_EVENT1 register.  Drop
 >> that.

 > Are you sure?  Sometimes 2 reads are required.  How was this tested?

Hard to be 100% sure, but the code did not have a double read before the
above commit and sticking a printk in the driver like this:

diff --git a/drivers/usb/typec/tipd/core.c b/drivers/usb/typec/tipd/core.c
index 01db27cbf1d1..6687d192dbd4 100644
--- a/drivers/usb/typec/tipd/core.c
+++ b/drivers/usb/typec/tipd/core.c
@@ -536,8 +536,9 @@ static irqreturn_t tps6598x_interrupt(int irq, void *data)
                intev_len = TPS_65987_8_INTEVENT_LEN;

        ret = tps6598x_block_read(tps, TPS_REG_INT_EVENT1, event1, intev_len);
-
+       printk(KERN_ERR "1st: %llx %llx\n", event1[0], event1[1]);
        ret = tps6598x_block_read(tps, TPS_REG_INT_EVENT1, event1, intev_len);
+       printk(KERN_ERR "2nd: %llx %llx\n", event1[0], event1[1]);
        if (ret) {
                dev_err(tps->dev, "%s: failed to read event1\n", __func__);
                goto err_unlock;


and (un)plugging the USB cable I see:

[ 3267.257341] 1st: 3000008 0
[ 3267.262097] 2nd: 3000008 0

[ 3267.345179] 1st: 1000000 0
[ 3267.350512] 2nd: 1000000 0

[ 3267.388947] 1st: 1000000 0
[ 3267.393707] 2nd: 1000000 0

[ 3267.912112] 1st: 1000000 0
[ 3267.916872] 2nd: 1000000 0

[ 3268.049505] 1st: 1000000 0
[ 3268.054773] 2nd: 1000000 0

[ 3269.105173] 1st: 1000000 0
[ 3269.109970] 2nd: 1000000 0

[ 3280.049111] 1st: 3000008 0
[ 3280.053865] 2nd: 3000008 0

So I am fairly sure it is not needed.

-- 
Bye, Peter Korsgaard