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Date: Mon, 24 Aug 2026 11:08:25 +0200
From: Greg KH <gregkh@linuxfoundation.org>
To: PS10 PETER HONG =?utf-8?B?5rSq57m85r6k?= <peter_hong@fintek.com.tw>
Cc: mkl@pengutronix.de, mailhol@kernel.org, linux-can@vger.kernel.org,
	linux-kernel@vger.kernel.org, admin@dynetrex.com,
	stable@vger.kernel.org
Subject: Re: [PATCH] can: usb: f81604: fix struct f81604_int_data size
 mismatch
Message-ID: <2026082433-dynamic-overspend-8f32@gregkh>
References: <20260824082758.9118-1-peter_hong@fintek.com.tw>
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In-Reply-To: <20260824082758.9118-1-peter_hong@fintek.com.tw>

On Mon, Aug 24, 2026 at 04:27:58PM +0800, PS10 PETER HONG 洪繼澤 wrote:
> The struct f81604_int_data defines 9 bytes of interrupt data:
> - Byte 0: Status register (sr)
> - Byte 1: Interrupt register (isrc)
> - Byte 2: Interrupt enable register (ier)
> - Byte 3: Arbitration lost capture (alc)
> - Byte 4: Error code capture (ecc)
> - Byte 5: Error warning limit register (ewlr)
> - Byte 6: RX error counter (rxerr)
> - Byte 7: TX error counter (txerr)
> - Byte 8: Reserved (val)
> 
> The hardware sends exactly 9 bytes for the interrupt endpoint.
> However, the struct was defined with __aligned(4) attribute which
> caused the compiler to pad the struct to 12 bytes.
> 
> This causes a problem in f81604_read_int_callback() where the short
> URB check compares urb->actual_length against sizeof(*data). When
> sizeof(struct f81604_int_data) is 12 but the hardware only sends 9
> bytes, the check fails and valid interrupt messages are discarded.
> 
> This results in the driver only being able to transmit once because
> the TX complete interrupt is never processed.
> 
> Fix this by removing the __aligned(4) attribute so the struct size
> matches the actual hardware data size of 9 bytes.
> 
> Fixes: 88da17436973 ("can: usb: f81604: add Fintek F81604 support")
> Fixes: 7299b1b39a25 ("can: usb: f81604: handle short interrupt urb messages properly")
> Cc: stable@vger.kernel.org
> Signed-off-by: Ji-Ze Hong (Peter Hong) <peter_hong@fintek.com.tw>

Nit, doesn't match the From: line :(

Also, the first Fixes: tag isn't correct, it's the second one that
matters.

And wasn't this reported by someone already:
	https://lore.kernel.org/r/A3834A07-5639-4779-844F-C5843DFC3928@dynetrex.com
?

And yes, this patch does look correct.

thanks,

greg k-h