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[2001:14ba:a0db:1f00::8a5]) by smtp.gmail.com with ESMTPSA id v26-20020a19741a000000b0050beeea07f3sm146792lfe.4.2023.12.02.14.23.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 02 Dec 2023 14:23:25 -0800 (PST) Message-ID: <551382fc-4256-4e2f-974c-9b0f6814a8f8@linaro.org> Date: Sun, 3 Dec 2023 00:23:24 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 4/6] drm/msm/dsi: add a comment to explain pkt_per_line encoding Content-Language: en-GB To: Jonathan Marek Cc: freedreno@lists.freedesktop.org, Rob Clark , Abhinav Kumar , Sean Paul , Marijn Suijten , David Airlie , Daniel Vetter , Jessica Zhang , Konrad Dybcio , Jiasheng Jiang , "open list:DRM DRIVER FOR MSM ADRENO GPU" , "open list:DRM DRIVER FOR MSM ADRENO GPU" , open list References: <20231114225857.19702-1-jonathan@marek.ca> <20231114225857.19702-5-jonathan@marek.ca> From: Dmitry Baryshkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 16/11/2023 20:45, Jonathan Marek wrote: > On 11/15/23 2:38 AM, Dmitry Baryshkov wrote: >> On Wed, 15 Nov 2023 at 01:00, Jonathan Marek wrote: >>> >>> Make it clear why the pkt_per_line value is being "divided by 2". >>> >>> Signed-off-by: Jonathan Marek >>> --- >>>   drivers/gpu/drm/msm/dsi/dsi_host.c | 2 ++ >>>   1 file changed, 2 insertions(+) >>> >>> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c >>> b/drivers/gpu/drm/msm/dsi/dsi_host.c >>> index 66f198e21a7e..842765063b1b 100644 >>> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c >>> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c >>> @@ -877,6 +877,8 @@ static void dsi_update_dsc_timing(struct >>> msm_dsi_host *msm_host, bool is_cmd_mod >>>          /* DSI_VIDEO_COMPRESSION_MODE & DSI_COMMAND_COMPRESSION_MODE >>>           * registers have similar offsets, so for below common code use >>>           * DSI_VIDEO_COMPRESSION_MODE_XXXX for setting bits >>> +        * >>> +        * pkt_per_line is log2 encoded, >>1 works for supported >>> values (1,2,4) >>>           */ >>>          reg |= >>> DSI_VIDEO_COMPRESSION_MODE_CTRL_PKT_PER_LINE(pkt_per_line >> 1); >> >> Should we switch to ffs() or fls() instead? >> > > Just a ffs() on its own can be confusing as well (without the > information that only powers of two are possible), I think like this is > better. Sounds fair. Could you please then add `if (pkt_per_line > 4) drm_warn("pkt_per_line too big");` With that in place: Reviewed-by: Dmitry Baryshkov > >>>          reg |= >>> DSI_VIDEO_COMPRESSION_MODE_CTRL_EOL_BYTE_NUM(eol_byte_num); >>> -- >>> 2.26.1 >>> >> >> -- With best wishes Dmitry