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[84.106.84.65]) by smtp.gmail.com with ESMTPSA id a32-v6sm867389edd.54.2018.06.26.06.36.29 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 26 Jun 2018 06:36:29 -0700 (PDT) Subject: Re: simple-framebuffer enquire To: Michael Nazzareno Trimarchi Cc: artlomiej Zolnierkiewicz , linux-fbdev@vger.kernel.org, LKML References: <9fb661e6-482b-76e0-2af0-a62a70e5606d@redhat.com> From: Hans de Goede Message-ID: <233d6808-4d44-9e47-7e3f-4f35cf731706@redhat.com> Date: Tue, 26 Jun 2018 15:36:29 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 26-06-18 15:29, Michael Nazzareno Trimarchi wrote: > Hi > > to be more specific > > On Tue, Jun 26, 2018 at 3:06 PM, Michael Nazzareno Trimarchi > wrote: >> Hi >> >> On Tue., 26 Jun. 2018, 12:01 pm Hans de Goede, wrote: >>> >>> Hi, >>> >>> On 25-06-18 15:29, Michael Nazzareno Trimarchi wrote: >>>> Hi Hans >>>> >>>> In order to let it even registered the simplefb I have added this >>>> change. According on what I understand >>>> from the code seems that this is the way to acquire memory with the >>>> correct attribute >>>> >>>> diff --git a/drivers/video/fbdev/simplefb.c >>>> b/drivers/video/fbdev/simplefb.c >>>> index a3c44ec..7e61ce3 100644 >>>> --- a/drivers/video/fbdev/simplefb.c >>>> +++ b/drivers/video/fbdev/simplefb.c >>>> @@ -466,8 +466,8 @@ static int simplefb_probe(struct platform_device >>>> *pdev) >>>> >>>> info->fbops = &simplefb_ops; >>>> info->flags = FBINFO_DEFAULT | FBINFO_MISC_FIRMWARE; >>>> - info->screen_base = ioremap_wc(info->fix.smem_start, >>>> - info->fix.smem_len); >>>> + info->screen_base = arch_memremap_wb(info->fix.smem_start, >>>> + info->fix.smem_len); >>> >>> I'm not sure why you need this? wb certainly is not optimal >>> for a framebuffer, the existing wc mapping is really what you >>> want. >>> >> >> Well in this way raise a WARN and get a nice NULL on memory remap on imx6ull >> SoC >> > > [ 0.397484] WARNING: CPU: 0 PID: 1 at arch/arm/mm/ioremap.c:303 > __arm_ioremap_pfn_caller+0x80/0x1cc This is causes by a mismatch in memory attributes, which means the memory is already mapped by the kernel as regular RAM and may already be used for other purposes by the kernel! Memory used by a simplefb framebuffer must be reserved by the bootloader, so that it does not get used by the kernel as regular RAM. See e.g.: http://git.denx.de/?p=u-boot.git;a=blob;f=drivers/video/sunxi/sunxi_display.c Near the end of the file where the framebuffer RAM gets excluded from the memory-range reported to the kernel as usable RAM. Note this relies on the u-boot sunxi video code putting the framebuffer at the end of the RAM. Regards, Hans