linux-kernel - Re: [PATCH v4 2/2] usb: typec: ucsi_glink: Increase buffer size to support UCSI v2

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Message-ID: <a31ac6fd-929f-4001-8199-1b8730ccbadd@oss.qualcomm.com>
Date: Wed, 1 Oct 2025 11:42:46 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Anjelique Melendez <anjelique.melendez@....qualcomm.com>
Cc: heikki.krogerus@...ux.intel.com, gregkh@...uxfoundation.org,
        lumag@...nel.org, neil.armstrong@...aro.org, johan+linaro@...nel.org,
        quic_bjorande@...cinc.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v4 2/2] usb: typec: ucsi_glink: Increase buffer size to
 support UCSI v2

On 9/27/25 12:07 AM, Dmitry Baryshkov wrote:
> On Fri, Sep 26, 2025 at 11:19:13AM -0700, Anjelique Melendez wrote:
>>
>>
>> On 9/25/2025 2:43 PM, Dmitry Baryshkov wrote:
>>> On Wed, Sep 24, 2025 at 04:26:31PM -0700, Anjelique Melendez wrote:
>>>> UCSI v2 specification has increased the MSG_IN and MSG_OUT size from
>>>> 16 bytes to 256 bytes each for the message exchange between OPM and PPM
>>>> This makes the total buffer size increase from 48 bytes to 528 bytes.
>>>> Update the buffer size to support this increase.
>>>>
>>>> Signed-off-by: Anjelique Melendez <anjelique.melendez@....qualcomm.com>
>>>> ---

[...]

>>> I'd prefer it to be more explicit. Define an union of v1 and v2, fill
>>> common parts and version-specific parts separately.
>> Konrad also left a similar comment in this function "This code keeps the
>> 'reserved' field zeored out for v1, but it does so in a fragile and implicit
>> way :/" (https://lore.kernel.org/all/df671650-a5af-4453-a11d-e8e2a32bd1ab@oss.qualcomm.com/#t)
>>
>> So I figured I would try to get thoughts from the both of you :)
>>
>> We could have a union defined like so:
>> struct __packed ucsi_write_buf_req_msg {
>> 	struct pmic_glink_hdr   hdr;
>> 	union {
>> 		u8 v2_buf[UCSI_BUF_V2_SIZE];
>> 		u8 v1_buf[UCSI_BUF_V1_SIZE];
>> 	} buf;
>> 	u32                     reserved;
>> };
> 
> LGTM.

+1

Konrad