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Date:   Fri, 20 Jan 2023 10:50:51 -0800
From:   Benson Leung <bleung@google.com>
To:     Prashant Malani <pmalani@chromium.org>
Cc:     linux-kernel@vger.kernel.org, chrome-platform@lists.linux.dev,
        bleung@chromium.org
Subject: Re: [PATCH] platform/chrome: cros_typec_vdm: Fix VDO copy
Message-ID: <Y8rii5gRTsi5jEP9@google.com>
References: <20230113182626.1149539-1-pmalani@chromium.org>
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Hi Prashant,


On Fri, Jan 13, 2023 at 06:26:26PM +0000, Prashant Malani wrote:
> The usage of memcpy() affects the representation of the VDOs as they are
> copied to the EC Host Command buffer. Specifically, all higher order
> bits get dropped (for example: a VDO of 0x406 just gets copied as 0x6).
>=20
> Avoid this by explicitly copying each VDO in the array. The number of
> VDOs generated by alternate mode drivers in their VDMs is almost always
> just 1 (apart from the header) so this doesn't affect performance in a
> meaningful way).
>=20
> Fixes: 40a9b13a09ef ("platform/chrome: cros_typec_vdm: Add VDM send suppo=
rt")
> Signed-off-by: Prashant Malani <pmalani@chromium.org>

Reviewed-by: Benson Leung <bleung@chromium.org>


> ---
>  drivers/platform/chrome/cros_typec_vdm.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>=20
> diff --git a/drivers/platform/chrome/cros_typec_vdm.c b/drivers/platform/=
chrome/cros_typec_vdm.c
> index aca9d337118e..06f4a55999c5 100644
> --- a/drivers/platform/chrome/cros_typec_vdm.c
> +++ b/drivers/platform/chrome/cros_typec_vdm.c
> @@ -86,10 +86,12 @@ static int cros_typec_port_amode_vdm(struct typec_alt=
mode *amode, const u32 hdr,
>  		.command =3D TYPEC_CONTROL_COMMAND_SEND_VDM_REQ,
>  	};
>  	struct typec_vdm_req vdm_req =3D {};
> +	int i;
> =20
>  	vdm_req.vdm_data[0] =3D hdr;
>  	vdm_req.vdm_data_objects =3D cnt;
> -	memcpy(&vdm_req.vdm_data[1], vdo, cnt - 1);
> +	for (i =3D 1; i < cnt; i++)
> +		vdm_req.vdm_data[i] =3D vdo[i-1];
>  	vdm_req.partner_type =3D TYPEC_PARTNER_SOP;
>  	req.vdm_req_params =3D vdm_req;
> =20
> --=20
> 2.39.0.314.g84b9a713c41-goog
>=20
>=20

--=20
Benson Leung
Staff Software Engineer
Chrome OS Kernel
Google Inc.
bleung@google.com
Chromium OS Project
bleung@chromium.org

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