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[87.92.245.163]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b86ebfd007fsm1126590566b.31.2026.01.13.13.02.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 13 Jan 2026 13:02:10 -0800 (PST) Message-ID: <0919844a-9246-4bdc-979c-115ccc3995c2@oss.qualcomm.com> Date: Tue, 13 Jan 2026 23:02:07 +0200 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] drm/msm/dp: Avoid division by zero in msm_dp_ctrl_config_msa() To: Nathan Chancellor Cc: Konrad Dybcio , Rob Clark , Dmitry Baryshkov , Abhinav Kumar , Jessica Zhang , Sean Paul , Marijn Suijten , linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org, llvm@lists.linux.dev, patches@lists.linux.dev, kernel test robot References: <20260108-drm-msm-dp_ctrl-avoid-zero-div-v1-1-6a8debcb3033@kernel.org> <20260113205955.GA2893481@ax162> Content-Language: en-US From: Dmitry Baryshkov In-Reply-To: <20260113205955.GA2893481@ax162> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Proofpoint-ORIG-GUID: DbCliR-7kKN_MEynE_BYBGfSI4wV5mVA X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMTEzMDE3MiBTYWx0ZWRfX+GTBJ1GJ/STa vY0hLdutbQbbKyzKFTdgPdijWaBHSW28k4mU8Z5GVqp60bJIGIHjxUQoMawfnrIjFwZ2H4g/3so 4GTe+cc2DJz91tTTZBcVKQAKkPlH5zt0DN/v3r/jTJrsOfIvX6xb07VKCtUI8/PlqfRyawFx81K dbTsGhEqKB4lvnkfZNUUVVs16RH6gE40Cydjdw4xJZPNmGbYoPEo16/N25sJB6wAnpfIS9cGYGL BrDJywluSjfXmC85FLN5aRAALZba4aOdwuMj2Np6lHagKbMyvZNi9spaXX+1OPEnPJ0vNdfi2uV R9pZYN/ogZX0rLoDjRJjkHzKdi8V5V0IglJmERRcknjT22c1pid/TEKY6F8V9czmf2lhyOsdCsV C5O+yD9pDq6GMLxsuxap2xf3EGIH8aDyk7CiTJz7oTe+3+sFZ0/sG3LveXr8M8BgONZv1FF/HQB kUrNIgXbOyiUFfs7SDA== X-Authority-Analysis: v=2.4 cv=TMlIilla c=1 sm=1 tr=0 ts=6966b2d4 cx=c_pps a=JIY1xp/sjQ9K5JH4t62bdg==:117 a=+WgfKLcscl3VAWRHYO56eA==:17 a=IkcTkHD0fZMA:10 a=vUbySO9Y5rIA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VwQbUJbxAAAA:8 a=LpQP-O61AAAA:8 a=0--PztnLt7rTvDwXMSMA:9 a=QEXdDO2ut3YA:10 a=tNoRWFLymzeba-QzToBc:22 a=pioyyrs4ZptJ924tMmac:22 X-Proofpoint-GUID: DbCliR-7kKN_MEynE_BYBGfSI4wV5mVA X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2026-01-13_04,2026-01-09_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 malwarescore=0 bulkscore=0 adultscore=0 phishscore=0 clxscore=1015 lowpriorityscore=0 spamscore=0 suspectscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2512120000 definitions=main-2601130172 On 13/01/2026 22:59, Nathan Chancellor wrote: > On Mon, Jan 12, 2026 at 04:37:46AM +0200, Dmitry Baryshkov wrote: >> On Fri, Jan 09, 2026 at 10:06:29AM +0100, Konrad Dybcio wrote: >>> Dmitry, would it be beneficial to throw an actual error when the rate is >>> is mangled? i.e. >>> >>> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c >>> index aa2303d0e148..4f710b8e6bc6 100644 >>> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c >>> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c >>> @@ -2404,9 +2404,9 @@ static int msm_dp_ctrl_link_retrain(struct msm_dp_ctrl_private *ctrl) >>> return msm_dp_ctrl_setup_main_link(ctrl, &training_step); >>> } >>> >>> -static void msm_dp_ctrl_config_msa(struct msm_dp_ctrl_private *ctrl, >>> - u32 rate, u32 stream_rate_khz, >>> - bool is_ycbcr_420) >>> +static int msm_dp_ctrl_config_msa(struct msm_dp_ctrl_private *ctrl, >>> + u32 rate, u32 stream_rate_khz, >>> + bool is_ycbcr_420) >>> { >>> u32 pixel_m, pixel_n; >>> u32 mvid, nvid, pixel_div = 0, dispcc_input_rate; >>> @@ -2415,14 +2415,21 @@ static void msm_dp_ctrl_config_msa(struct msm_dp_ctrl_private *ctrl, >>> u32 const link_rate_hbr3 = 810000; >>> unsigned long den, num; >>> >>> - if (rate == link_rate_hbr3) >>> + switch (rate) { >>> + case link_rate_hbr3: >>> pixel_div = 6; >>> - else if (rate == 162000 || rate == 270000) >>> - pixel_div = 2; >>> - else if (rate == link_rate_hbr2) >>> + break; >>> + case link_rate_hbr2: >>> pixel_div = 4; >>> - else >>> + break; >>> + case 270000: >>> + case 162000: >>> + pixel_div = 2; >>> + break; >>> + default: >>> DRM_ERROR("Invalid pixel mux divider\n"); >>> + return -EINVAL; >> >> Well... In the ideal world, we can't end up here, PHY's >> configure_dp_clocks (or qcom_edp_set_vco_div()) will fail if the link >> rate is is invalid here. I think, we should return an error here, but >> there is no need to propagate it further. >> >> See the discussion at https://lore.kernel.org/dri-devel/f2ce6ae51c50b0d2e57b905c63b43413@codeaurora.org/ > > I interpret that as approving of the above hunk but omitting the hunk > that modifies msm_dp_ctrl_on_stream(). In that case, what is the point > of changing the return type of msm_dp_ctrl_config_msa()? Wouldn't the > below diff have the same exact effect as a smaller change? I don't mind > rolling this up as a v2. > > Cheers, > Nathan > > diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c > index aa2303d0e148..d8ea73b89f7c 100644 > --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c > +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c > @@ -2409,20 +2409,27 @@ static void msm_dp_ctrl_config_msa(struct msm_dp_ctrl_private *ctrl, > bool is_ycbcr_420) > { > u32 pixel_m, pixel_n; > - u32 mvid, nvid, pixel_div = 0, dispcc_input_rate; > + u32 mvid, nvid, pixel_div, dispcc_input_rate; > u32 const nvid_fixed = DP_LINK_CONSTANT_N_VALUE; > u32 const link_rate_hbr2 = 540000; > u32 const link_rate_hbr3 = 810000; > unsigned long den, num; > > - if (rate == link_rate_hbr3) > + switch (rate) { > + case link_rate_hbr3: > pixel_div = 6; > - else if (rate == 162000 || rate == 270000) > - pixel_div = 2; > - else if (rate == link_rate_hbr2) > + break; > + case link_rate_hbr2: > pixel_div = 4; > - else > + break; > + case 162000: > + case 270000: > + pixel_div = 2; > + break; > + default: > DRM_ERROR("Invalid pixel mux divider\n"); > + return; Please add a comment, stating that we can't actually reach it. LGTM otherwise. > + } > > dispcc_input_rate = (rate * 10) / pixel_div; > -- With best wishes Dmitry