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AJvYcCVIUarQuzVKK0t6uXnni8vl0g1nPncaf378ySlZSgMmyUpmIx8XDfGoEMEV5R/yiSCXGAAI8jjKseztixqZpThMeH1BV6mvEknv34tR X-Gm-Message-State: AOJu0YyfIDoak2qLNOROd3F2UViXqWxyx6VapLA4C6nDtrQOSw+dR+15 e0ZkRZ+61Oj9DWcbGEdvEDrc1sZLHpYwQrei0RFEC5YrwjdpIazbEhUXF2keBEtsFSrDAHLxhTw cBC9uLdc7KnfWwb7IWPF+i0XRvKk/zjj0nI+XWCk3wnylwcYhX40= X-Received: by 2002:a25:8104:0:b0:de5:852f:6afe with SMTP id o4-20020a258104000000b00de5852f6afemr1262062ybk.30.1713995359592; Wed, 24 Apr 2024 14:49:19 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20240418081548.12160-1-lvzhaoxiong@huaqin.corp-partner.google.com> <20240418081548.12160-3-lvzhaoxiong@huaqin.corp-partner.google.com> In-Reply-To: From: Dmitry Baryshkov Date: Thu, 25 Apr 2024 00:49:08 +0300 Message-ID: Subject: Re: [PATCH v1 2/2] drm/panel: kd101ne3: add new panel driver To: Doug Anderson Cc: Hsin-Yi Wang , lvzhaoxiong , mripard@kernel.org, airlied@gmail.com, daniel@ffwll.ch, robh@kernel.org, krzysztof.kozlowski+dt@linaro.org, conor+dt@kernel.org, dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, cong yang Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 25 Apr 2024 at 00:04, Doug Anderson wrote: > > Hi, > > On Tue, Apr 23, 2024 at 2:20=E2=80=AFPM Dmitry Baryshkov > wrote: > > > > On Tue, Apr 23, 2024 at 01:41:59PM -0700, Doug Anderson wrote: > > > Hi, > > > > > > On Tue, Apr 23, 2024 at 11:10=E2=80=AFAM Hsin-Yi Wang wrote: > > > > > > > > > > > > +#define _INIT_DCS_CMD(...) { \ > > > > > > > > + .type =3D INIT_DCS_CMD, \ > > > > > > > > + .len =3D sizeof((char[]){__VA_ARGS__}), \ > > > > > > > > + .data =3D (char[]){__VA_ARGS__} } > > > > > > > > + > > > > > > > > +#define _INIT_DELAY_CMD(...) { \ > > > > > > > > + .type =3D DELAY_CMD,\ > > > > > > > > + .len =3D sizeof((char[]){__VA_ARGS__}), \ > > > > > > > > + .data =3D (char[]){__VA_ARGS__} } > > > > > > > > > > > > > > This is the third panel driver using the same appoach. Can yo= u use > > > > > > > mipi_dsi_generic_write_seq() instead of the huge table? Or if= you prefer > > > > > > > the table, we should extract this framework to a common helpe= r. > > > > > > > (my preference is shifted towards mipi_dsi_generic_write_seq(= )). > > > > > > > > > > > > > The drawback of mipi_dsi_generic_write_seq() is that it can cau= se the > > > > > > kernel size grows a lot since every sequence will be expanded. > > > > > > > > > > > > Similar discussion in here: > > > > > > https://lore.kernel.org/dri-devel/CAD=3DFV=3DWju3WS45=3DEpXMUg7= FjYDh3-=3Dmvm_jS7TF1tsaAzbb4Uw@mail.gmail.com/ > > > > > > > > > > > > This patch would increase the module size from 157K to 572K. > > > > > > scripts/bloat-o-meter shows chg +235.95%. > > > > > > > > > > > > So maybe the common helper is better regarding the kernel modul= e size? > > > > > > > > > > Yes, let's get a framework done in a useful way. > > > > > I'd say, drop the _INIT_DELAY_CMD. msleep() and usleep_range() sh= ould be > > > > > used instead (and it's up to the developer to select correct dela= y > > > > > function). > > > > > > > > > > > > > > > > > > > + > > > > > > > > +static const struct panel_init_cmd kingdisplay_kd101ne3_in= it_cmd[] =3D { > > > > > > > > + _INIT_DELAY_CMD(50), > > > > > > > > + _INIT_DCS_CMD(0xE0, 0x00), > > > > > > > > > > [skipped the body of the table] > > > > > > > > > > > > > + _INIT_DCS_CMD(0x0E, 0x48), > > > > > > > > + > > > > > > > > + _INIT_DCS_CMD(0xE0, 0x00), > > > > > > > > > > > > > + _INIT_DCS_CMD(0X11), > > > > > > > > > > Also, at least this is mipi_dsi_dcs_exit_sleep_mode(). > > > > > > > > > > > > > + /* T6: 120ms */ > > > > > > > > + _INIT_DELAY_CMD(120), > > > > > > > > + _INIT_DCS_CMD(0X29), > > > > > > > > > > And this is mipi_dsi_dcs_set_display_on(). > > > > > > > > > > Having a single table enourages people to put known commands into= the > > > > > table, the practice that must be frowned upon and forbidden. > > > > > > > > > > We have functions for some of the standard DCS commands. So, mayb= e > > > > > instead of adding a single-table based approach we can improve > > > > > mipi_dsi_generic_write_seq() to reduce the bloat. E.g. by moving = the > > > > > error handling to a common part of enable() / prepare() function. > > > > > > > > > > > > > For this panel, I think it can also refer to how > > > > panel-kingdisplay-kd097d04.c does. Create the table for init cmd da= ta, > > > > not what operation to use, and use mipi_dsi_generic_write_seq() whe= n > > > > looping through the table. > > > > > > Even more similar discussion: > > > > > > https://lore.kernel.org/r/CAD=3DFV=3DUGDbNvAMjzWSOvxybGikQcvW9JsRtbxH= Vg8_97YPEQCA@mail.gmail.com > > > > It seems I skipped that thread. > > > > I'd still suggest a code-based solution compared to table-based one, fo= r > > the reasons I've outlined before. Having a tables puts a pressure on th= e > > developer to put commands there for which we already have a > > command-specific function. > > The problem is that with these panels that need big init sequences the > code based solution is _a lot_ bigger. If it were a few bytes or a > 1-2KB then fine, but when Hsin-Yi measured Linus W's attempt to move > from a table to code it was 100K difference in code [1]. I would also > say that having these long init sequences done as separate commands > encourages people to skip checking the return values of each of the > transfer functions and I don't love that idea. > > It would be ideal if these panels didn't need these long init > sequences, but I don't have any inside knowledge here saying that they > could be removed. So assume we can't get rid of the init sequences it > feels like we have to find some way to make the tables work for at > least the large chunks of init code and encourage people to make the > tables readable... I did a quick check on the boe-tv101wum-nl6 driver by converting the writes to use the following macro: #define mipi_dsi_dcs_write_cmd_seq(dsi, cmd, seq...) \ do { = \ static const u8 d[] =3D { cmd, seq }; = \ ret =3D mipi_dsi_dcs_write_buffer(dsi, d, ARRAY_SIZE(d)); = \ if (ret < 0) = \ goto err; = \ } while (0) And then at the end of the init funciton having err: dev_err(panel->dev, "failed to write command %d\n", ret); return ret; } Size comparison: text data bss dec hex filename before 34109 10410 18 44537 adf9 ./build-64/drivers/gpu/drm/panel/panel-boe-tv101wum-nl6.o making init data const 44359 184 0 44543 adff ./build-64/drivers/gpu/drm/panel/panel-boe-tv101wum-nl6.o with new macros 44353 184 0 44537 adf9 ./build-64/drivers/gpu/drm/panel/panel-boe-tv101wum-nl6.o As you can see, there is literally no size difference with this macro in pl= ace. The only drawback is that the init stops on the first write rather than going through the sequence. WDYT? I can turn this into a proper patch if you think this makes sense. > > > [1] https://lore.kernel.org/r/CAD=3DFV=3DUFa_AoJQvUT3BTiRs19WCA2xLVeQOU= =3D+nYu_HaE0_c6Q@mail.gmail.com --=20 With best wishes Dmitry