From mboxrd@z Thu Jan 1 00:00:00 1970 From: Heiko Schocher Date: Tue, 26 May 2015 07:29:54 +0000 Subject: Re: [RFC PATCH] video/logo: introduce new system state for checking if logos are freed Message-Id: <556420F2.7020909@denx.de> List-Id: References: <1430896145-8887-1-git-send-email-hs@denx.de> <5562B9CE.7050807@ti.com> <5563EEF9.3080901@denx.de> <556418A9.8010603@ti.com> <55641D89.5020103@ti.com> In-Reply-To: <55641D89.5020103@ti.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Tomi Valkeinen Cc: Geert Uytterhoeven , "linux-kernel@vger.kernel.org" , Linux Fbdev development list , Jean-Christophe Plagniol-Villard Hello Tomi, Geert, Am 26.05.2015 09:15, schrieb Tomi Valkeinen: > > > On 26/05/15 10:08, Geert Uytterhoeven wrote: >> On Tue, May 26, 2015 at 8:54 AM, Tomi Valkeinen wrote: >>> On 26/05/15 06:56, Heiko Schocher wrote: >>>>> Without locking, the initmem may be freed while fb_find_logo() is >>>>> running. >> >> Or afterwards. Drivers may keep the pointer around indefinitely. >> >>>> Yes, you are right, that must be added ... but has such a change a >>>> chance to go in mainline? >>> >>> I don't know. To be honest, this whole thing feels a bit like hackery. I >>> think initdata should only be accessed from initcalls, never asynchronously. >>> >>>> BTW: Could this not be currently a problem on multicore systems? >>>> If lets say core 2 just draws the logo, another core 1 calls >>>> fb_logo_late_init() and later core 1 free_initmem(), while the core 2 >>>> still draws it? >>> >>> Yes, I think so... >> >> I don't think that can happen. All initcalls should complete before initmem >> is freed. > > Ah, true, the question was only about the initcalls. I was answering to > what actually can happen with the logo code as a whole. > > The whole problem started when I fixed an issue where the logos were > accessed from a workqueue. I don't remember the details, but I think drm > always (?) sets up some console stuff via workthread. In that case we > could have the workthread accessing the logos, while initmem is being freed. > >>> So, maybe it would be better to not even try to go forward with the >>> current approach. Two approaches come to my mind: >>> >>> 1) Keep the logos in the memory, and don't even try to free them. I >>> don't know many bytes they are in total, though. >> >> m68k/allmodconfig: >> >> $ size drivers/video/logo/logo*o >> text data bss dec hex filename >> 24 6961 0 6985 1b49 drivers/video/logo/logo_linux_clut224.o >> 24 800 0 824 338 drivers/video/logo/logo_linux_mono.o >> 24 3200 0 3224 c98 drivers/video/logo/logo_linux_vga16.o >> 24 6955 0 6979 1b43 drivers/video/logo/logo_mac_clut224.o >> 161 4 2 167 a7 drivers/video/logo/logo.o >> >> Not that bad... Custom logos may be larger, though. > > I wonder how much a simple RLE would cut down the sizes... > >>> 2) Make a copy of the logos to a kmalloced area at some early boot >>> stage. Then manually free the logos at some point (after the first >>> access to the logos? after a certain time (urgh...)?). >> >> 3) Draw the logos from an initcall on all frame buffers that exist at that >> point in time. Yes, this will destroy (part of) the content that's >> currently shown. > > Isn't that almost the same as now? The problem is that the fb probes are > deferred to a very late stage, so we would not have the fbs when the > suggested initcall would be called. Yes, exactly, this is my problem. DRM gets probed early and returns with EPROBE_DEFER, as the display needs a spi init sequence, but spi is not running yet ... later, when spi is up, DRM probes again, and all is fine, but the logo is not drawn, as fb_logo_late_init() is called before, which prevents drawing the logo. We maybe could call fb_logo_late_init() directly from init/main.c before calling free_initmem() ? But here again the question, could it be possible that another core just draws the logo? Or does async_synchronize_full() helps us here? bye, Heiko -- DENX Software Engineering GmbH, Managing Director: Wolfgang Denk HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany